Based on cloud-top brightness temperature data and circulation background, and the physical quantities, Diagnosis of severe convection weather caused by MCS in Mei-yii front over the Yellow Sea-Changjiang River during June 21 to 23, 2002 is made. The results show that the MCS is main system of the heavy rainfall in Mei-yufront over Changjiang River Basin. There is close relationship between the heavy rainfall center and the high occurrence frequency center of convection and deep convection. The frequency of F_M(T_BB≤-32℃)and F_S (T_BB≤52℃) can reflect the characteristics of rainfall well and better than the low value center of T_BB. In addition, the severe heavy rainfall was caused by the interaction among Mei-yu front, lower level shear line and upper level Tibet high.