Haloxylon ammodendron, Tamarix ramosissima and Nitraria tangutorum are widely used sand-fixing shrubs in sandy desert areas. They are well adapted to sandy conditions. However, the understanding on the patterns of stem sap flow of the three shrubs is poor. The diurnal and seasonal variations of sap flow were measured with Stem Heat Balance(SHB), and the simultaneous weather factors were observed at a nearby automatic weather station from May to October in 2006. The results showed that the starting time of sap flow was species-specific and varied with stem diameters within a species. The sap flow of H.ammodendron stems with basal diameters of 1.70cm, 3.64cm and 5.07cm started at 5:00-7:00, 5:00-7:20 and 6:00-8:00, respectively. That of T. ramosissima stems with 1.57cm and 3.03cm basal diameters started at 5:20-7:20 and 5:40-7:40, and that of N. tangutorum stems 1.59cm basal diameters started at 6:00-8:00. The diurnal variations of sap flow showed a bi-peaked curve for H. ammodendron, and a multi-peaked curve for T. ramosissima and N. tangutorum. The maximum velocity of sap flow appeared during 11:40-13:20 for H. ammodendron, 12:40-13:00 for T. ramosissima and 12:00-13:00 for N. tangutorum. All of the three species had an ambiguous noon-depression phenomenon of the sap flow curves. There was sap flow occurred at night for the three shrubs, but the duration of the flow at night varied with stem diameters. The larger the stem diameter, the longer the duration of sap flow at night. The sap flow of the three shrubs at night had an obvious decreasing course and approached zero prior to the sap flow started next day. The seasonal variations of sap flow for the three shrubs showed a unimodal pattern, in which the highest value occurred in August for H. ammodendron and T. ramosissima, and in July for N. tangutorum. During the entire growing season, the unit area sap flow intensity for the three shrubs with similar stem diameters ranked as N. tangutorum ﹥T. ramosissima ﹥H. ammodendron from high to low, which implied that the drought tolerance of H. ammodendron was higher than that of N. tangutorum and T. ramosissima. The results showed that vapor pressure deficit or air temperature was the major weather factor affecting sap flow for H. ammodendron, and solar radiation for T. ramosissima and N. tangutorum, which indicated that the weather factors played different roles in affecting sap flow of the three shrubs.