Based on monthly precipitation data from May to September 1970-2022 from 80 weather stations, methods such as the IDW space interpolation method, Mann-Kendall test, cumulative anomaly method, and wavelet analysis were used to analyze the rainfall trends, periodicity, and mutation characteristics of precipitation during the flood season. The results show: (1) In recent 53 years, the average flood precipitation amount is 459.2 mm, with the most at 784.1 mm (in 2016) and the least at 317.6 mm (in 2007). The flood precipitation has shown a slight trend of increasing at a rate of 2.5 mm/a. (2) The precipitation in flood season reflects obvious intergenerational variation characteristics, mainly in a "W" variation trend, with the average flood precipitation in each decade showing 2000s < 1970s < 1980s < multi-annual average < 1990s < 2010s. (3) The mid part of the province in Yichun, north of Hegang and the middle of Harbin had the highest flood rainfall, the lowest was in the Great Khingan Mountains, the Songnen Plain, and the Sanjiang Plain. The spatial distribution from west to east was characterized by a "lowhigh-low" distribution. (4) There were three time scales, 54, 17, and 6 years, with the first period, the most intense one, being the first primary period. The main cycle of precipitation in flood season is 34a, the sub-cycles are 12a and 4a. (5) The cumulative distance showed a "decline -fluctuate -rise" trend. The flood season precipitation had an abrupt change in 2011 and showed a change from less to more, post-mutation 2012-2022 compared to pre-mutation 1970-2011, the mean increase was 142.5 mm.