Abstract: This paper takes Hongze Lake in the lower reaches of Huaihe River system as the research object and divides the flood season into different stages,the method of rainfall time-area-depth analysis and calculation is adopted and it is based on the daily rainfall data of more than 1 000 rainfall stations with continuous records and uniform distribution since 1990, according to the flood season division standard of the Ministry of Water Resources, the calculation period is selected as 3 d, and the cumulative rainfall standard is 30/50 mm, this paper adopts the index of the dynamic change of 3 d cumulative rainfall coverage area of the Huai River and analyzes the date of the flood season and the main flood season. As a large plain lake located in the lower reaches of the Huai River system, Hongze Lake receives water from the upper and middle reaches of the Huai River. In this paper, the runoff data of seven stations entering Hongze Lake from 1990 to 2019（a total of 30 years） are synthesized, and the daily synthetic flow is calculated by fractal analysis and change-point analysis, flood season and main flood season of Hongze Lake are obtained by comprehensive analysis. The flood season of Huaihe River system is from May 23 to September 17 according to time-area-depth analysis of rainfall, among which the main flood season is from June 26 to August 28. The flood season of Hongze Lake is from May 25 to September 30 according to Fractal analysis method, among which the main flood season is from June 20 to August 20; the flood season of Hongze Lake is from May 1 to September 28 according to change point analysis, among which the main flood season is from June 19 to August 28. The results are comprehensively analyzed and can be used to provide a basis for the classification of Hongze Lake in flood seasons and the setting and dispatching of control water level in flood seasons.