Abstract: In hydrology, the form of the rainstorm intensity formula is known as the nonlinear one with excess factors, and its parameters are not easy to be solved with normal methods, which makes the method design of parameters estimate and the elimination of the error from parameters estimate the most crucial. For a long time, many methods to estimate the parameters of the formula have been put forward by hydrological and meteorological experts that have exerted a profound influence on urban water drainage design. But all the methods above have certain error from objective error by personal judging, approximate supposed error, or missing error from skip-over searching.An objective and optimized method for estimating the parameters of the rainstorm intensity formula is put forward that can avoid the above errors skillfully. First, the non-linear formula is linearized and the scope of the parameters b and C is decided. Second, the parameters A and n can be determined based on known rainstorm intensity, duration and return period (i-t-T) tri-relation table by least regression method after the value of b (single period formula) or a combination of the value of b and C(multi-period formula) is given. Then the formula with least error is the optimum one.This method is used in Shenzhen and Wuhan separately, and the accuracy of the formula can meet the requirement of the national standard and is superior to the compared methods. A software has been designed according to the new method and can be used easily and popularized nationwide. If the original data are put in, the estimating result of the curve pattern, formula parameters, error, figures and table can be obtained quickly.