Using NCEP-FNL data, we analyzed a continuous heavy rain process in Hangzhou Bay, and found that the constant intersection of cold and warm flows in Zhejiang Province caused the continuous rainfall. The increase of lowlevel cold air and southeast warm and humid air resulted in the development of baroclinic atmosphere disturbance, the enhancement of rainfall in the frontal area and the occurrence of heavy rains. Due to the deviation of the numerical model forecast, a large error occurred in the 24 h forecast of heavy rainfall in Hangzhou Bay during this process. The test results showed that the GFS model is better for the prediction of the cold and warm system in 36 h lead time, but has an error for the wind forecast in the low-level front, which affected the convergence, horizontal frontogenesis and the transportation of water vapor in the lowmiddle layer, leading to the deviation of falling area of heavy rain and rainstorm. In addition, it is also an important factor in the rainstorm forecast error that the model is weak in forecasting cold air in the south bank of Hangzhou Bay. Therefore, for rainfall stability forecast, forecasters need to attach importance to model adjustment in the prediction at adjacent time, and judge the influence of cold and warm air flow according to actual monitoring and the movement and evolution of rain belt, so as to timely adjust the rainfall zone and influence time and make an effective correction to forecasts.