Based on the MPL(micro pulse lidar) data over Shouxian area(32°33'30.18"N,116°46'55.02"E),Anhui Province from 14 May to 28 December 2008,this paper analyzes the diurnal variation of mixed layer height(MLH).Comparisons are made between MLHs retrieved by MPL retrieval methods(the gradient method,the inflection point method and the normalized gradient method) and MLH determined by the sounding data measured by SONDE.Results show that MLH retrieved from the lidar data using the gradient method are highly correlated with MLH measured by SONDE(the correlation coefficient is 0.976),and the gradient method is the most suitable retrieval algorithm in Shouxian area.The diurnal cycle of MLH on sunny days are retrieved by the gradient method,and the effect of meteorological conditions on MLH are also studied.Results show that the growth rate of MLH agrees well with the hourly increase of surface temperature one hour before.Surface wind speed and direction can also lead to rapid change of MLH.The development of MLH exhibits temporal behavior similar to that of the aerosol optical thickness,but with 0.5—3 h lag time.