Abstract: The Weigan irrigated is located in an alluvia-l diluvial plain in the northern part of Tarim Basin, and its elevation varies in a range of 920～1, 100 m a. s. l. Climate here is extremely dry, the annual precipitation is only 51.6 mm, the annual evaporation from water surface, however, varies in a range of 1992.0～2863.4 mm. It is rich in sunshine and solar heat resources, the annual temperature changes in a range of 10.5～11.4℃, and light soil and sandy soil are the main soil types in the irrigated area. Weigan River is its only irrigation water source, and land evaporation is the main water consumption. Currently there are many methods for calculating land evaporation, however, the parameters needing in some calculating methods are difficult to determine. In this paper, land evaporation in the Weigan irrigated area (4, 130.3 km²) is estimated by using water budget method, Turk empirical formula, and reduction coefficient method based on the available data. The results are as follows：
(1) In the Wergan irrigated area, the annual land evaporation is 576 mm, it is 8. 7 times higher than the annual precipitation (67 mm), which is one of the results of human activities, such as water diverting for irrigation.
(2) The evaporation mechanism in the irrigated areas in arid regions is mainly conrolled by water supply conditions, and land evaporation is the main consumption of water resources in arid regions. Land evaporation occupies 89. 4% of the total water loss in the Weigan irrigated area, of which 99% are surface water.
(3) Land evaporation estimated by water budget method is reliable and can be regarded as the standard to calibrate the precision of that estimated by other methods. The relative error of land evaporation estimated by water-heat budget method varies in a range of 4%～10%. The empirical formula used for estimating land evaporation with reduction coefficient method is as ：E-0.30 E 20, the reduction coefficient is 0.30, and the comprehensive coefficient of land evaporation is 0.49. These show that land evaporation in the oasis irrigated areas in arid regions can be estimated by water-heat budget method and can also be calculated by evaporation from water surface.

Key words: Weigan River, irrigated area, land evaporation, estimation