Based on the conventional observation data, automatic weather station data, wind-profiling radar and CINRAD-SA Doppler radar data as well as ERA-Interim 0.125°×0.125° 6 h reanalysis data, the extreme severe rain occurring in the west area of Fujian on 19 May 2015 was analyzed. The results show that the extreme severe rain process included two stages: warm area precipitation and frontal precipitation. The heavy rain area located in the left of south-west jet. Sufficient water vapor, the confluence of cold and warm air, the strengthening of unsteady convective stratification, decrease of lifting condensation and free convection height and moderate vertical wind shear over the rainstorm-hit area were all favorable to the development of MCS. During the warm area precipitation, southwest airflow was converged on the southwest side of rainfall area. The air with sufficient water vapor and high energy was lifted by the cold outflow air near the mesoscale boundary. New convective cells generated continuously. The convective cells moved to the east-northeast and formed a short rain belt. Several NE-SW short oriented rainbands established on the north side of the outflow boundary, moving eastward slowly and affecting the rainfall area repeatedly. Convergence line and wind speed convergence over the rainstorm area provided a good dynamic lifting condition for precipitation. The convective cells were strengthened by the valley topography opening to the southwest. The continuous back-building of convective cells and several NE-SW oriented rainbands were two major developing modes of MCS. During the frontal precipitation, with the shear of low-level vortex moving eastward and southward, new convective cells were born in the region of wind speed convergence, water vapor and high energy and moved southeast. Northwest wind of middle and high level showed forward tilting feature. The vertical wind shear increased. The confluence of cold and warm air caused rainfall strengthening and maintenance. Backward prorogation and eastward moving of convective cells forming train effect was the main developing mode of MCS.