The causes of a local extraordinary rainstorm in the northwestern Changde on 24 August 2006, by means of Doppler radar and Lightning data，is analyzed. The results indicate that the continual formation and combination of MCV (Mesoscale Convective Vortex) maintained the life cycle of MCC (Mesoscale Convective Complex), and three MCCs formed an organized MCS (Mesoscale Convective System); this heavy rain was caused mainly by the mesoscale convergence line; the generation and development of radar echoes inclined to the direction of the warmwet airflow; the southeast warm and wet airflow provided sufficient vapor; the beginning of lightning activity indicated the beginning of the heavy rain; the lifting effect of the southtonorth terrain favored the maintenance and reinforcement of the rainstorm and enhanced and prolonged the rainstorm.