The paper establishes a model of rural-urban migration on the basis of the maximization of the net income of labor allocation, and ushers in variables as system, living costs and non-agricultural industries in rural areas. It also analyzes the non-permanent rural-urban migration, and makes a theoretical analysis on various influencing factors of such migration on the basis of the model. Data from ad hoc surveys are used in the empirical test to part of these influencing factors.