The city is the result of the development of the history.And the ancient capitals are the especial group of cities.The site selection of the ancient capital is not only the same to general cities but also has itself peculiar point.This paper talks about the influence factors of the site selecting by taking examples of the site selection of Xi'an and Beijing.Then we know that the influencing factors of the site selecting include geographical environment,geographical terrain,climate conditions,and the political meaning of being capital,but the last one is the essential reason.