Abstract: Using the Weather Research and Forecasting(WRF) model and its 3-Dimension Variational assimilation system(WRF-3DVar) a torrential rain case occurred in Yunnan Province is simulated and studied.The results indicate that the WRF-3DVar can reasonably reflect the relationships among multivariable and availably.In the case the WRF-3DVar availably assimilate the information of low-level jet to the initial condition of regional numerical model,further more reasonably distribute the wind increment as model.The assimilation of the retrieved wind data help to strengthen water vapor transportation and improve the veracity of forecast precipitation.In addition the more times data assimilation improve rain forecast accuracy more clearly,so the retrieved wind data have a good referenced value and outlook in the weather forecast,which have higher frequency observation.