Twenty processes of the Meiyu front with heavy rain over the Changjiang-Huaihe Valley are analysed by using Q divergence. The distribution and characteristics of the Q divergence on the middle and low layers in troposphere in Meiyu front are studied,the space-time relationship between the belt of heavy rain and the main weather system on the middle and low layers in troposphere is also studied. The results show that Q divergence is comparatively reasonable for forecasting of the area of heavy rain on Meiyu front over Changjiang-Huaihe Valley.