Based on the long series of measured precipitation data of Dantu station from 1981 to 2016, Mann-Kendall test was used to analyze the variation trend of maximum annual precipitation with four medium and long durations of 3, 6, 12 and 24 hours. Fuzzy identification method was adopted to identify the rainfall pattern characteristics of four duration rainstorms. The design rainfall in different durations and return periods was calculated based on the optimized distribution function. According to five typical rainstorms, the same frequency method and Pilgrim & Cordery method were used to deduce the corresponding design rainstorm process and comparative analysis was conducted. The results show that although the maximum annual precipitation of four durations all showed increasing trends to different degrees, only the maximum annual precipitation of 6 h and 12 h passed the 90% significance test. The rainfall patterns of four duration rainstorms were all dominated by single peak with a slight front. P-Ⅲ distribution function fitted optimally in rainfall frequency analysis. The peak value obtained by the same frequency method was larger than that obtained by Pilgrim & Cordery method, which was beneficial to ensure flood control safety.