Planning design for preventing waterlogging in tide-affected area must reasonably determine the design process of tidal level combined with the design rainfall in waterlogging area, while the upstream flood will raise the tide level in the drainage receiver, having especially effects on the raising of lower tide level, which is very unfavorable for the use of the gate to rush the drainage water, so the coincidence between the rainfall in the waterlogging area and the upstream flood in the drainage receiver needs to be analyzed. Taking Zhong-Zhu union catchment as an example, the qualitative analysis and the probabilistic risk analysis are adopted respectively to analyze the coincidence rules of the rainfall of Zhong-Zhu union catchment and the flood in the upstream of Modaomen waterway in the drainage receiver. The results of the qualitative analysis show that during the period from May to August every year, when there is a heavy rain in Zhong-Zhu union catchment, it is likely to encounter the flood from XiJiang River, especially during June to July. The results of the probability risk analysis show that when there is a rainstorm with a return period of no less than 20 years and no rainstorm with a return period of more than 20 years, and the probability of maximum flood with a return period of no less than 90%, 75%, multi-year average, 5-year and 10-year is 15.21%, 10.99%, 6.58%, 4.12%, 2.93% and 13.62%, 9.80%, 5.84%, 3.65% and 2.59%, respectively.