In order to improve the single-station precipitation forecast accuracy, a case study was conducted on a strong precipitation event on 19 July 2003 in Hubei Province. Through diagnostic analysis, the causes of circulation formation were discussed. The results show that it was a typical large-scale heavy rain process resulted from a mid-latitude barocline system, and its formation mechanism can be explained by the quasi-geostrophic theory. For strong precipitation forecast, especially severe heavy rainfall forecasts within or at the edge of the raining area, secondary circulation must be diagnosed and analyzed. Only when the conditions of the secondary circulation are met, heavy rainfall will occur; or else there will be an absent forecast.