Based on conventional observation data, automatic weather station data, and NCEP reanalysis data, a severe squall line occurred in Zhejiang Province on 5 May 2016 is simulated with high-resolution numerical model WRF. The results show that the shear line is the main weather system inducing the severe squall line process. The squall line occurred under the atmosphere condition of abundant water vapor, weak convective available potential energy, and moderate vertical wind shear. WRF model performs well as simulating the evolution of the squall line and the precipitation distribution. Through further analysis of the simulation data, it is found that thunderstorm high and surface cold pool are important boundary layer characteristics of the squall line, and the boundary layer convergence line is beneficial to the development and maintenance of the squall line. The strong downdraft below the middle troposphere behind the squall line is the key factor causing the thunderstorm gale.