Abstract:The 7·20 Zhengzhou severe heavy rain broke the historical records of Zhengzhou observed station's daily precipitation (552.5mm) and 1-hour precipitation (201.9mm) since the station was established. It was also a catastrophic rainfall process causing hundreds of deaths and dozens of missing. This severe rainfall was characterized as high intensity, wide coverage and along-terrain distribution. This study use gauge precipitation observations, geostationary satellite observations, reanalysis data and multiple numerical model forecast data to analyze the causes of models’ forecast deviation and the ability of Jiangsu Precision Weather Analysis and Forecasting System (PWAFS) in extreme rainfall forecasting in this process. The main conclusions are as follows: (1) The heavy rain was caused by the strengthened easterly flow between the westward extended subtropical high and the intensified typhoon "In-fa", as well as the uplifting effect of topography. The former provided the vapor conditions and the latter provided part of the dynamic conditions; (2) European Center for Medium- range Weather Forecasts(ECMWF)and Global Forecast System(GFS) had a good performance in heavy rain location but the precipitation center was slightly northerly biased and the intensity was noticeably lower than observation. PWAFS had a better performance in precipitation intensity forecast and had a distribution pattern along the terrain. However, PWAFS shows a west bias of isolated rain center. (3) Through the analysis of the PWAFS forecasts and reanalysis data, it was found that on 20 July over the heavy rain area, there was a shear line eventually developed into a deep low-pressure system, which provide favorable dynamic conditions contributing to the convection development.