On May 28, 2016, a disastrous rainstorm occurred along the western coast of Guangdong Province. Using the conventional observation data such as regional automatic station, Doppler radar and NCEP / NCAR reanalysis data, this paper analyzes the evolution characteristics and maintenance mechanism of mesoscale weather system of this precipitation process.The results show that: (1) the rainstorm occurred in the southwest jet of the monsoon trough, which provided unstable energy for the rainstorm. At the same time, sufficient water vapor content, significant water vapor convergence and vertical helicity of 20×10-6hPa·s-2 are conducive to the formation, development and maintenance of the heavy rainfall system.(2) The analysis of mesoscale convective system (MCS) shows that MCS (b) and MCS (c) are the main systems causing the precipitation. After the two systems are formed at the same time, they merge and strengthen rapidly, and maintain at the same place with little movement. The analysis of radar data shows that the heavy rainfall has obvious backward propagation and train effect. The radar echo is a mixed precipitation echo mainly composed of cumulus clouds, which has the characteristics of high efficiency and long time.(3) The analysis of the surface data of regional automatic stations shows that the new convective cloud clusters and the large temperature gradient on the north and south sides of the convergence line are continuously stimulated along the coastal mesoscale convergence line, which provides a good lifting trigger condition for the occurrence and development of heavy rainfall. At the same time, the "trumpet mouth" topography along the coast of Jiangmen and Yangjiang strengthens the convection.