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Based on the conventional data, automatic weather station data, Doppler radar observational data, etc., the causes of two heavy rainfall events occurred on 18 June and 7 July 2010 in the mountainous northwestern Fujian are compared and analyzed. The results show that both of the two processes happened under the circulation condition of the southwardmoving cold air guided by the eastmoving upperlevel trough and the interaction of the southwest jet with the strong wind speed convergence over the northern and central Fujian, integrating with rich water vapor, strong vertical ascending motion, and unstable atmosphere stratification. The position of the subtropical high, the horizontal width of the southwest jet, and the forwardtilting trough are the important influencing factors of the duration and scope of the heavy rainstorm. The storm strength is positively correlated with the vertical ascending motion and the suction effects of lowerlevel convergence and upper level divergence, etc. The maximum center of water vapor flux and water vapor flux divergence over the storm zone appeared earlier than heavy rainfall. The variation of water vapor has indicative significance for the forecasting and early warning of disasters weather. The radar echoes of the two rainstorms exhibit a zonal distribution, and the moving direction of the strong radar echo intensity center is consistent with the long axis of the echo center.