By using conventional observation data、dual polarization radar data、 ERA5(0.25o^×0.25o) reanalysis data,the weather background、environmental conditions、triggering mechanism of mesoscale convective system、radar parameter characteristics of the two extreme rainfall processes in Zhejiang on July 16 and 22, 2023 are compared and analyzed,the result show that：(1)The two processes occurrs in a similar circulation background of 500hPa with westerly trough moving eastward around the Subtropical High, and the typhoon or tropical depression in the South China Sea. Both processes are triggered by the surface mesoscale convergence line.(2)The background of middle-low and precipition area are different,process 1 occurs in cold shear at 850hPa and the rainfall center is located at the edge of the Subtropical High,while process 2 occurs in consistent southwest airflow at 850hPa and the rainsfall center is located in Subtropical High circulation.(3)The thermal and dynamic conditions are different,the extreme rainfall of process 1 occurs in the process of 850 and 925hPa southeast airflow enhancement, the boundary layer airflow is more significant, the atmospheric stratification is unstable,