Abstract: Feng-Yun 3A is the first satellite with microwave humidity sensor (MWHS),which can provide data for numerical weather forecasting on global and regional scales.This paper focused on assessing the effects of FY-3A MWHS data assimilation on relative humidity analysis and forecasting by using a 3D-Var data assimilation system coupling WRF model.The results show that the MWHS data assimilation improves relative humidity analysis,and obtains better relative humidity analysis compared to the NOAA AMSU-B data assimilation.In general,the method using the MWHS data assimilation improves the relative humidity forecasting accuracy compared with the method using the AMSU-B data assimilation.For 18 hour forecasting results,the humidity forecasting accuracies at 400 hPa,600 hPa and 800 hPa levels using the MWHS data assimilation method are higher than those using the AMSU-B data assimilation method.These results indicate that the FY-3A MWHS has a wide application prospect in numerical weather forecasting.