The populous County Shuyang County has been borrowing nearby city's rainstorm formula. It is necessary to compose its own formula of rainstorm intensity to provide scientific basis for the planning and design of urban drainage and waterlogging system. In this paper, based on the precipitation data of Shuyang county collected for 35 years from 1981 to 2015, 11 annual rainfall maximum were selected as the measured samples. Based on the P-Ⅲ distribution, exponential distribution and Gumbel distribution, the theoretical frequency curve analysis is carried out to determine the recurrence period-rainfall intensity to the time (P-i-t) relationship table, and to calculate the storm intensity formula. By drawing the new formula and the old formula of rainstorm intensity~period curve the comparative analysis was made The results show that the difference between the two models is large, so it is necessary to compose the formula of rainstorm intensity in Shuyang county.