The contribution of conventional observations on the east side of Tibetan Plateau to forecast error in WRF model is evaluated by using the WRFDA-FSO(Forecast Sensitivity to Observation) system from May to October in 2009 and 2010.Results show that,for the surface observations,the surface temperature contributes the major impact to the forecast error,the surface wind,surface pressure and water vapor contribute the minor impact,and the surface observations located in the regions(including eastern of Sichuan,most of Guangxi,and south edge of Yunnan) contribute the positive impact.For the sounding observations,the sounding temperature contributes the major impact to the forecast error,the sounding water vapor and sounding wind contribute minor impact,and the sounding observations located in the regions(including most of Yunnan,west edge of Guizhou,and northwest edge of Guangxi) contribute positive impact.After removing the surface and sounding observations,which contribute negative impact,the precipitation and temperature forecast are improved.