A heavy rainstorm process occurring simultaneously at the northern and southern piedmont of the Qinling Mountains from August 21 to 22， 2021 is compared and analyzed to explore the influence mechanism of the triggering conditions at the northern and sorthern piedmont of the Qinling Mountains by using the real-time meteorological observation data， FY-2G satellite cloud images， doppler radar data and ERA5 0.25°×0.25° hourly reanalysis data.The result shows that on the flow field of the northern piedmont of the Qinling Mountains， the westerly system forms a meso-scale cyclonic circulation in the lower troposphere under the special topography of the Qinling Mountains， which triggers heavy rainfall through thermal effects.Convective precipitation is short-lived and its intensity is weak.The enhancement of wet baroclinicity is a signal of the beginning of the rainstorm at the northern Qinling Mountains.The precipitation ends when the wet baroclinicity weakens and the specific humidity of the middle layer decreases.For the southern piedmont of the Qinling Mountains， the formation of mesoscale convergence lines in the lower tropospheric flow field under the effect of topography triggers the rainstorm.The condensation latent heat released by precipitation heats the lower atmosphere and establishes a convective instable structure， together with the cold intrusion in the middle and lower layers， which leads to the enhancement of the upward movement and the precipitation.Under the high temperature and humidity environment， the convective cloud organizes and develops rapidly to form the MCC， which has a high convective intensity， deep convective tropospheric junctions， and powerful hourly rainfall.The timing of the invasion and diffusion of cold air in the lower and middle layers to the ground represent the beginning and end of heavy rain at the sorthern Piedmont of the Qinling Mountains respectively.