In operational weather forecast, the short-term heavy precipitation under the control of the western Pacific subtropical high is easily to be missed. In order to get a better grasp of short-term heavy rainfall in Hunan under the control of the western Pacific subtropical high and explore its causes and trigger mechanism, this paper analyzes a short-term heavy rainfall process on September 6, 2018 by using the observation data from ground automatic weather station and Doppler weather radar, retrieved TBB (black body temperature) from FY-2F satellite and NCEP reanalysis. The results show that the abundant water vapor, stronger unstable energy and certain uplift conditions can trigger the short-term heavy rainfall in Hunan Province in the ridge of the strong western Pacific subtropical high. However, it is more difficult to forecast the rainstorm due to the lack of large-scale circulation systems such as trough, middle and low level jet and shear line. Due to the invasion of weak cold air before noon, the cooperation of low-level shear with surface mesoscale convergence line cause near surface dynamic uplift, further trigger convective precipitation. In the afternoon, the surface air temperature affecting by solar radiation reaches convective triggering temperature, which can trigger freely heat convection. Both the positive vorticity region and the low-level convergence region extend upward after the rainfall, which is conducive to the maintenance of vertical upward movement, but its dynamic condition is obviously weaker than that of typical heavy precipitation process in flood season. The environmental wind and its vertical shear are weak, and the thunderstorm cells move slowly, which is beneficial to the maintenance of heavy rainfall for a long time in the same area.