the core of urbanization is citizenization, with the main body of migrant workers' citizenization. It is worthwhile to study how to get the maximal gaining in the fast urbanization of China. This paper divides the issue in two parts. The first part, through constructing mathematical models, tries to find the standard determining the optimal urbanization time, and makes the theoretical analysis under the standard. The second part makes an empirical conclusion based on the condition in China: the urbanization begins late in China, which leads to a low gaining. Thus the paper proposes a differentiation policy of citizenization, optimizing the structure of financial expenditure, and improving the official examination system.