The method of Set Pair Analysis is to study the certain and uncertain relationship between the different things and the key of this method is to calculate the connection degree of these things. In order to assess the urbanization levels, this paper proposed a new method to establish the assessment standards according to the value of assess indexes. The urbanization level of Yangtze River delta cities was assessed by Set Pair Analysis, and the results calculated are generally consistent with Nonlinear Mapping Analysis and Factor Analysis. Set Pair Analysis can provide an effective solution to urbanization assessment. The proposed method of standards establishment and Set Pair Analysis can also be used in other areas without unified assessment standards.