In August 2017, there were torrential rains in Longnan, Gansu Province. The 24-hour precipitation at the Li County and

Wudu weather stations broke through the historical extreme values, with obvious extremes and localities. Based on ERA5 reanalysis data of the European Centre for Medium-Range Weather Forecasts, radar data and ground observation data, a comparative analysis of two heavy rain cases that occurred in Longnan, Gansu Province from 6 to 7 and from 19 to 20 August 2017 are carried out. The circulation background and the radar reflectivity factor, radial velocity and physical quantity characteristics of the heavy rainfall processes of the two cases are discussed emphatically. The results show that the two rainstorms all occurred at the intersection between the northerly airflow in the westerly trough and the southerly warm and humid airflow in the middle-lower layer, but the main impact systems and triggering conditions are different. The radar echo shows from August 6 to 7, the convective system caused by the cold shear line is stronger, with higher reflectivity factor, lower central height, higher precipitation rate and shorter duration. The reflectivity factor of precipitation in warm region from August 19 to 20 is lower, and its central height is higher, and the precipitation rate is smaller, and the precipitation process maintained for longer time.