Abstract:The Tarim desert highway protection forest grows in the hyperarid Taklimakan Desert. Therefore，irrigation and water use are crucial for a sustainable management of this protection forest．In a protected part of the forest near the Tarim Desert highway, stem sap flow and water use of Haloxylon ammodendron were measured using the heat-balance technique．The stem sap flow exhibited a distinct diurnal course with maximum values between 10:00 to 15:00，and minimum values between 00:00 to 03:00．Generally, sap flow was lower at night than during the day．The sap flow was influenced by environmental factors：it was positively correlated with solar radiation，air temperature and wind speed，and negatively correlated with the relative humidity．Under the present irrigation scheme，the soil moisture remained almost constant，and was not correlated with sap flow．In Haloxylon ammodendron，the values of predawn and midday water potential provided no indications of drought stress．The average daily water use of three individuals of Haloxylon ammodendron with a diameter of 2.0 cm，2.8 cm and 3.4 cm were 1.48 kg，2.18 kg and 3.08 kg，respectively，amounting to an annual water consumption of 295 kg，436 kg and 616kg．The good water status of Haloxylon ammodendron indicated that the water supply to the protection forest by the present water management is sufficient．When sufficiently irrigated，Haloxylon ammodendron used a relatively large amount of water，what was also caused by the extremely arid environment.