Based on the conventional data, GFS reanalysisi data, and satellite images of FY 2C, two MCC processes in 2007 are analyzed, with emphasis on the environmental flow and synoptic physical conditions. The results demonstrate: several mseo β and meso α scale cloud clusters intensified and merged, from which the MCCs formed; the MCCs developed in the favorable environmental field, with the trough in the middle layer, the warm cold shear and the broad warm wet airflow in the lower layer. The enhancement of the southwestward warm wet airflow and the formation and maintenance of the warm shear line in the lower layer were the key factors to MCC formation; the joint influencing of cold air and moist warm flow led to energy frontogenesis. The coupling of frontogenesis in lower layer and its associated strong divergence in the right rear of the high level jet were the main dynamical mechanisms of MCC formation. There existed anticyclone divergence flow in the upper layer, and cyclone convergence flow in the middle lower layer, and the vertical vorticity column supplied favorable dynamical mechanism in the rainstorm centre.