Abstract：This article analyses the generalization of case study in its entirety. The analytic hierarchy adopts a structure from logic, to basis of logic, to significance by degrees. It is to encourage people to deepen the understanding of the generalization of case study that the author puts statistical investigation into every hierarchy. By analyzing Robert Yin’s sequential interview, Fei Xiao-tong's approach of classification comparison, Geertz’s thick description, Burawoy's extended case method, and Wang Fuwei’s relational case study, the logic of them can be concluded as “case study logic” and “falsification logic”. Then, it is be discovered that basis of the logic of generalization is derived from population thinking between case study and statistical investigation. In population thinking, case study can describe population heterogeneity lightly and depict the knowledge causing of deviation exactly, statistical investigation can explain population heterogeneity better. Contributions and limitations can co-exist in the significance of the generalization of case study; case study promotes accumulations about knowledge of population with statistical investigation in a hypothesis diagram of social sciences research which consisted of case study and statistical investigation. There is no perfect method to study social sciences because of its complexity, which is applies to case study, too. The greatest significance of case study is to be able to play a valuable role in the appropriate research objectives.