Humble Administrator’s Garden is a precious heritage of garden art, and the change of its entrance space directly affects the visitors’ experience. Therefore, the study of the entrance space characteristics of Humble Administrator’s Garden in different periods has specific enlightenment significance for protecting ancient garden buildings and the entrance space design of modern gardens. Based on the perspective analysis method, using the parametric software grasshopper, this paper makes a quantitative comparative analysis of the entrance space series of the Humble Administrator’s garden in three different periods. The relevant indicators include the max diam, var radial, iosvist area, circularity, drift, etc. And then, it studies and summarizes the influence of the change of its spatial structure on the spatial horizon and tourism experience.