Abstract: The topic about alien is always interesting. The novels and films about aliens have also caused the reverie of the masses. The problem of my research paper is weather the alien exit. By consulting astronomical data on the official website of NASA, I find some circumstantial evidence of the Aliens are more likely to exit than not exit. Through the discussion of the possibility of the existence of aliens, I finally concluded that in the vast universe, the existence of aliens is very likely. Although we have never found any traces of their existence, but from the scale of the universe, the possibility of the existence of aliens is certain. In the research paper, the arguments about the aliens may exist provide a basis for the existence of aliens and change people’s traditional understanding of the aliens.Key word: Alien Exit Life Planet Aliens are more likely to exist than not As human beings have made remarkable achievements in astronomical observation and space industry, people are increasingly interested in planets and creatures outside the earth. The discussion of the life of the earth and the extraterrestrial life is also embodied in literature and film and television works. Whether the aliens exist is one of the most discussed topics. There’s a lot of disagreement about this topic. Because it related to people’s attitude towards the existence of aliens, such as some people who with strong religious beliefs or science-fiction writers. There are many people agree with that there are aliens in the universe, while the others have the opposite attitude. When they happened to be together, we will find some interesting points and reasons. But in fact, we have no enough obvious evidence that aliens exist to prove it, of course, we can ‘t prove that aliens do not exist yet. What we can do is to discuss aliens are more likely to exist than not or contrary. It is obvious that we will also misread the word itself sometimes. Because in different cases, aliens refer to different meaning, such humanoid alien life, alien life, the alien higher intelligent life. So, before we talk about it, let ‘s make it clear that aliens refer to alien life with advanced intelligence in this context. In the following discussion, I will in-depth discuss gradually why aliens are more likely to exist from the perspective of modern scientific cosmology, biology, probability theory and modern astronomical observations.First, earth is a very special as a planet as a planet that born of life, but not very special that only earth has the conditions for the birth of a living planet. In modern scientific research, scientist agreed with the theory that life on Earth had its beginnings in a prebiotic environment (NASA, 1985). It means the life on earth was naturally occurring in a special organic environment. Of course, the organic environment is also naturally occurring by a series of processes. It shows that the earth as a birth of life and human civilization is not unique in that the earth is chosen by god ‘s children, but the earth has the conditions for the birth of life and human civilization. As the same time, other planets are also likely to be as lucky as earth to have the similar natural conditions for life as earth. Although the environment that can produce life is not likely to be owned by every planet, we can’t deny the possibility completely.Second, life on Earth is the only known life in the universe, but there are convincing data to suggest we are not alone (Neil deGrasse Tyson,2017). There are so many planets in the universe that beyond our imagination, that the possibility of the life on earth is the only life in the universe is negligible. A rough estimate from a survey by the PLANET (Probing Lensing Anomalies NETwork) collaboration, which was founded in 1995 would point to the existence of more than 10 billion terrestrial planets across our galaxy. (NASA Content Administrator, 2017) In the same year, Hubble’s Ultra Deep Field revealed a myriad of faint galaxies. This led to an estimate that the observable universe contained about 200 billion galaxies (Karl Hille Mathias Jaeger, &Christopher Conselice, 2017). It shows that the universe is so big and there is a great possibility that other planets, like earth, have the similar conditions to produce life. Make a rough calculation, 200 billion multiplied by 10 billion is 20 billion trillion, an unbelievable number, it shows that there are about 20 billion trillion terrestrial planets across our universe. More or less. Some people maybe still have a negative attitude towards this point of view. Let’s do a little calculation. If only 1 per cent of these planets are at a suitable distance from the stars, 1 per cent of the remaining 1 per cent have a reasonable chemical composition, water is produced in 1 per cent of the remaining 1 of 10,000 planets, and organic matter is produced in only 1 per cent of the remaining 1of 1000,000 planets, there will be still a very considerable number of planets which are meet the conditions of life, about 200 trillion. So, it is more likely that there are many living planets in the space than not, in other words, the living on the earth isn’t alone. Third, some scientific researchers have discovered some organic matter from extraterrestrial cosmic objects which may provide an evidence for the existence of many planets in the universe that meet the conditions of life. For example, the Tagish Lake meteorites which is a large meteoroid exploded in the atmosphere over northern British Columbia, Canada, and rained fragments across the frozen surface of Tagish Lake in January 2000. There is a paper about the analysis of the meteorite fragments published June 10 in the journal Science. A team discovered the fragments of the Tagish Lake meteorites contained an assortment of organic matter including amino acids, which are the building blocks of proteins. Proteins are used by life to build structures like hair and nails, and to speed up or regulate chemical reactions (Bill Steigerwald, 2011).”We’ve never seen this kind of variability from a single parent asteroid before. Only one other meteorite fall, called Almahata Sitta, matches Tagish Lake in terms of diversity, but it came from an asteroid that appears to be a mash-up of many different asteroids.” Said Dr. Daniel Glavin of NASA Goddard, who is a co-author on the Science paper (Bill Steigerwald, 2011).