Abstract: The synoptic causes and mesoscale convective characteristics of a short-time heavy rainfall process were analyzed, which occurred in Yunnan Province from 20:00 on September 5 to 20:00 on September 6, 2017, based on the observational data of satellites, radars, ground automatic stations and lightning locators. The results show that the distribution of short-time heavy rainfall areas gradually shifted from northeast to southwest, which indicated obvious characteristics of systematic precipitations. The shear line on 700 hPa and the cold front on the ground are the key influencing systems of this case. The shear line provided a mechanism for maintaining water vapor convergence and convective uplift in the middle layer; and the cold front provided a triggering mechanism for the convective uplift in the lower layer. The spatial scale and duration of meso-scale convective cloud clusters well indicated the distribution and scale of short-term heavy rainfall, because the short-time heavy rainfall events mainly occurred in the areas with cloud top brightness temperatures below −50 ℃. If the convective cloud clusters have a large spatial scale and long duration, the short-time heavy rainfall in corresponding periods will be wide and frequent. Radar observation is helpful for fine forecast correction and early warning of short-time heavy rainfall weather. When the radar echo intensity reaches and exceeds 45 dBz and has obvious low center characteristics with a meso-scale convergence of radial velocity, short-time heavy rainfall will follow in the same area.