Abstract: To investigate the mesoscale characteristics and trigger mechanism of one warm-zone torrential precipitation (WZTP) over complex terrain from 16 to 18 August 2012, the conventional observation data, precipitation data of automatic weather stations, TBB data of FY-2E and NCEP 1°×1° reanalysis data are synthesized and analyzed. The results show that the WZTP happened in the transitional zone between Eastern slope of Tibet Plateau and Sichuan Basin, and distributed zonally as a belt. Maximum hourly precipitation was loacaled at the area where TBB gradient of MCS increased efficiently. The circulation situation of the WZTP are contributed mainly by the typhoon moving westward in the South China Sea and the steadying Subtropical High. Then, the Subtropical High and warm low-pressure near the surface could prevent the westerlies trough and cold air moving across the Longmen Mountain. As a result, the unstable stratification with high energy and temperature over precipitation region can maintain for a longtime. Furthermore, the convergence of the cold and temperature advection over Longmen Mountain increased the instability of unstable stratification. At last, the torrential precipitation are triggered by the orography dynamic lifted by Longmen Mountain.