Abstract: This article analyzes the classification and usage of exits and entrances of the underground space. It is indicated that the exits and entrances have their multiple functions. These functions can be grouped into two kinds, one is the functions of those involving with means of communication and emergency escape; the other is the functions of those creating good apperance and environment. Based on the indicated functions,the auther puts forward a criterion of good design which is to make the functions clear and get the space multi-used.