Abstract: Flood encounter in the main stream and tributaries, tributaries and tributaries, upper and lower reaches aggravate the severe situation of flood control in the upper reaches of the Yangtze River.The frequent occurrence of rainstorm and flood disaster in the basin seriously affects the stable development of the coastal area. It is necessary to analyze the law and situation of flood encounter comprehensively and systematically. Based on the hydrological statistical analysis method, the flood encounter rules of ten different combinations of the main stream and tributaries, tributaries and tributaries, upstream and downstream of the upper Yangtze River Basin are analyzed from the aspects of flood encounter times and time, peak encounter and magnitude of maximum 7-day and 15-day flood process encounter, and maximum 7-day and 15-day flood process overlap days. Then the severity of flood peak, the severity of maximum for 7 days and 15 days flood process, and the overlap degree of maximum for 7 days and 15 days flood process are sorted and analyzed by using the improved five-element connection number set pair situation sorting method.The results show that, when a flood happens, the overall situation of peak and flood volume of various flood combinations in the upper reaches of the Yangtze River is not serious, but the overlapping degree of the maximum 7-day and 15-day flood processes is at a high level, which shows that the flood lasts for a long time and the process flood volume is large. In particular, the overlapping degree of the maximum 7-day flood volume of Wujiang River and the mainstream of the Yangtze River at Yichang Station is especially serious, which brings great flood control pressure to Yichang Station and its downstream Jingjiang flood diversion area. The improved fiveelement connection number set pair potential ranking method retains 181 logically established potential levels, quantitatively depicts the connection trend between flood encounter indicators and severity levels from the angles of equal potential, balance of potential and reverse potential, and quantifies the severity of flood encounter into different potential levels meticulously and accurately, which is helpful to quickly judge flood control priorities and provide a decision-making basis for implementing scientific dispatching.