An analysis is made of the evolution characteristics of a MCS during a torrential rain in Sichuan and Chongqing, using the conventional observation, automatic ground station, wind profiler, Doppler radar, and NCEP/NCAR 1°×1° reanalysis data. The results show that: (1) The torrential rainfall and MCS exhibited the evolution features of enhancingreducingenhancing again during the rain. Heavy precipitation supercells and mesoscaleγ cyclones appeared in the MCS enhancement phase. (2) The MCS was generated and maintained inside the ascending branch of the secondary circulation in front of Southwest Vortex, which moved eastward slowly and enhanced continuously and provided favorable background dynamic conditions for the longterm maintenance of the MCS. (3) The fluctuating evolution characteristics of the MCS are not consistent with the persistent enhancement characteristics of Southwest Vortex. The fluctuating evolution of the MCS was related to the changes of Southwest Jet or South Jet in the low and middle levels and the warmwet inflows in the low level and on the ground. The enhancement of the Southwest Jet or South Jet in the lower and middle levels and the enhancement of the warmwet inflows in the lowlevel and on the ground all provided favorable conditions for the enhancement of MCS.