On the basis of the routine weather charts, numerical prediction products, satellite cloud pictures and the V3θ diagram from the breakingupevolving theory, the regional continual rainstorm process occurred in Gansu to the northeast of the Tibetan Plateau from 30 June to 2 July 2005 is diagnosed and analyzed. The results show that during the heavy rainfall,the subtropical high pressure extended to west and lifted the external southwest current to north, which controlled the northeast party of the QinghaiXizang Plateau; when the Mongolia vortex, the westerly cold airflow and the southwest wind converged, a strong convection was triggered; there was a deep water vapor level between 850 hPa and 200 hPa and a stable vortex shear on 700 hPa, providing continuously strong rising movement for the heavy rainfall; and several Mesoscale Convective Systems (MCSs) appeared successively on the satellite cloud pictures. It is concluded that the prediction method based on the breakingupevolving theory is capable of forecasting the beginning, ending and areas of continuous heavy rainfall in the Northwest China.