The accuracy of rainstorm intensity formula directly affects the design of city water supply and drainage pipeline network. The original rainstorm intensity formula for Hefei City was determined in the 1970s which has been unable to meet present requirement in the precision and standardization. For the urgent need to revise a new formula, the precipitation data at the Dongpu Station in Hefei City from 1965 to 2012 were analyzed. All the data were taken with the annual maximum sampling method, and the fitting was made by using the method of Pearson-Ⅲ type of distribution,exponential distribution and Gumbel distribution. In order to determine the parameters of the formula, 6 optimization algorithms such as Levenberg-Marquart algorithm, Gauss-Newton method, quasi-Newton method, genetic algorithm, simulated annealing algorithm and particle swarm algorithm were used. Finally, the best formula was ascertained with exponential distribution maching Marquart algorithm. The accuracy is greatly improved relative to the original formula. The new formula can be used in many fields such as risk analysis of flood disasters and design of city water supply and drainage pipeline network. This new formula has great significance to prevent waterlogging, drainage, drainage facilities planning and engineering design of Hefei City.