An ensemble forecast and a deterministic forecast of a squall line that occurred in southern China on 23 April 2007 have been conducted using the Weather Research and Forecasting (WRF) model with microphysical schemes that include complex ice and snow processes.It is found that the deterministic forecast can capture the main characteristics of the squall line,but the simulated squall line is inaccurate,especially in the back stratus cloud region.The ensemble forecast technique can reduce the uncertainty in the model simulation and the majority of the members in the ensemble show a better performance than the deterministic forecast.The analysis members,which are obtained from radar data assimilation using the EnSRF (Ensemble Square Root Filter) method with outputs of the 40 members in the ensemble experiment as backgrounds,are used to provide initial conditions for the ensemble forecast.Differences in results among the ensemble members with and without radar data assimilation reflect the impact of EnSRF radar data assimilation on the simulation of the squall line.The analysis members with radar data assimilation provide more mesoscale and microscale information of the convective cells in the squall line system.Most members can capture the thermal-dynamical structure of the squall line system and successfully simulate the suqall line in the back stratus cloud region.Analysis of the simulations in the ensemble forecast with radar data assimilation indicates that most members perform better than that without radar data assimilation.The ETS (Equitable Threat Score) of the ensemble forecast with radar data assimilation is higher than that without radar data assimilation,and the ETS of the deterministic forecast is lower than that of the ensemble forecast.