P-III has been widely used by many scholars to fit precipitation, and the results are good. The Z-index assume that the precipitation accord with the distribution. It is a common method to response the spread and grade of drought and flood. In practical applications ，Z-index need correct due to that it is not suitable to the reality because of rainfall features in some regions. In this paper, precipitation was selected in represen - tative weather stations in seven zones (the North China, Central China, East China, South China, Northeast China, Northwest China and Southwest China) to analyze rainfall frequency features and revised the boundary value of Z-index. The results show that the boundary value of Z-index is different due to rainfall feature, especially in the North China and South China.