The impact of desert afforestation on weather modification western Australia was studied focusing oil precipitation increase. A three-dimensional spectral mesoscale model was used to Simulate limited-area weather modification by changing surface conditions including surface wetness, roughness, and albedo. Using global analysis data sets as the initial and boundary conditions, comparative simulations were made for original and modified surface conditions in the region of 500 (.) 500 km under typical conditions of clear days and rainy days in four seasons. The results show that precipitation is enhanced by the surface modification in all the cases studied on rainy days in summer, in particular, precipitation increase amounted to more than the evaporation increase, through a mechanism by which strong solar radiation evaporates water from the afforested area to cause a wet upstream, which stimulate the low pressure coming from outside. The mechanism, of precipitation increase as indicated in this study provides an efficient watering policy to save the precious water resource in arid land.