Recently, the substance of social space has been influenced due to the growing of population and differential of income in Taichung and it has resulted in residential differentiation. Therefore, the phenomenon has reflected in the discrepancy of social space as well as the unequal distribution of social resource. The purpose of the study is to find out the reasons and condition on the differentiation of social space of Taichung. So these issues are applied through "factorial analysis" to determine the causes of the social differentiation of Taichung, which is based on the theories of "Social area analysis" and "Urban factorial ecology". And then, using "Cluster analysis" examine the differentiation condition of social space. The results show that the cause-factors of social differentiation are "the characteristics of occupations and composition of the population", "the characteristics of migrant population", "the social economic group of high income family", "the slum communities", "the social-economic group of middle income family", "the retirement population", "the lack of green spaces and public facilities" and "the social-economic group of low income family". And that have divided Taichung city into four groups: 1. "The low-income residential area" is distributed in the inner city area of Taichung city; 2. "The middle low-income residential area" is mainly located in the southern part of Taichung city; 3. "The middle-high income residential area" is established around the suburban area which provides large open spaces; 4. "The high-income residential area" gathers in the Quan-guo commercial area. Comparing the space stuectures of Taichung City in 1989 and 1999, it is found that the social space pattern has been changed quite a lot.