In 21 and 22 May 2012, a heavy rainstorm process happened in Guizhou Province, which was a typical MCS triggered process, caused by the frontogenesis of type Ⅲ stationary front, under the guidance of a southern trough. The MCS was non linear with severe rainfall. Analysis reveals that the stationary front was strong; the frontogenesis process was obvious with a high energy tongue and a low vortex shear at the front, and a southerly jet on the south side. In the vertical direction, the front had a steep frontal area and strong upward motion, which was caused by the southern trough, the forward lean distribution, and the convective instability of the convex. These characteristics are beneficial to MCS: the high energy tongue and low vortex shear provide thermal and dynamic conditions for MCS, and the southerly jet is also an important factor. In the vertical direction, the convex area was important, and the distribution of θse and the forward lean distribution were beneficial. The moisture conditions in the front of and on the front were sufficient. Moisture convergence at the exit of the southerly jet and upward flow were sufficient to supply the moisture for MCS and the heavy rainstorm.