Abstract: In order to study the relationship between water use efficiency and soil water and light of 4 local tree species in Qinghai, the authors used Li-6400 photosynthetic apparatus to measure the net photosynthetic rate and transpiration, and calculated the water use efficiency. The results showed that: the 4 drought resistant tree species in Qinghai obtained the maximum water use efficiency when the soil moisture was from 16% to 18%, and the photosynthetic active radiation was between 1300 and 1600 μmol/(m²·s). Comparing the water use efficiency of Reaumuria sorgarica Maxim., Elaeagnus angustifolia Linn., Sabina vulgaris and Junipreus scopulorum under the same soil moisture condition, it showed that Elaeagnus angustifolia Linn. had higher water use efficiency than the other 3 tree species, even in drought soil environment. The results indicated that although the 4 drought resistant tree species in Qinghai were able to adapt to drought environment, but Elaeagnus angustifolia Linn. got stronger adaptability to the extremely arid area in plateau. Therefore, drought resistance tree species and fast-growing tree species could be used together in afforestation, to alleviate the lack of tree species in desert area and realize the re-green work in desertification land.