In order to choose proper sand-fixing shrub species and vegetation water management in Mu Us sandy land,stem sap flow of Atraphaxis bracteata was measured by using heat-balance packaged stem sap flow measuring system and simultaneously,related environmental impact factors were observed with automatic weather station system in Yanchi County,Ningxia Hui Autonomous Region from May to September in 2009and 2010.Results showed that:（1）Diurnal dynamics of the sap flow of Atraphaxis bracteata presented a significant regularity.Changing course of the sap flow velocity presented a multi-peak curve with obvious diurnal change.（2）In the growing season,the sap flow velocity of Atraphaxis bracteata changed with its growth stage.In the early growth period of Atraphaxis bracteatain May and June,the sap flow velocity was relatively low because of low soil moisture;in the vigorous growth period of Atraphaxis bracteata after rainy season in July and August,the sap flow velocity reached its maximum due to the increased cumulative soil water content;and in September,physiological process of Atraphaxis bracteataslowed down and consequently,the sap flow velocity decreased gradually.（3）The effects of environmental factors on the sap flow velocity were analyzed by using partial correlation method.Solar radiation was found to be the most important factor for the sap flow of Atraphaxis bractea,followed by atmospheric temperature,air relative humidity and wind speed.