This paper built the optimal multipart pricing model for the medium and small electricity customers applying with nonlinear pricing theory. This pricing model reflected the differences in demand characteristics between customers through differential pricing for different incremental purchase to guide the users to change the power consumption model, which could improve economic efficiency of pricing and increase energy efficiency. Then a self-selected two-part tariff was presented on the basis of the idea of separating equilibrium contract theory, which achieved equivalent effect to the above multipart model in the manner of customers' interaction. Finally example verified the validity of the models.