Abstract: Research of soil moisture before sowing(SMBS) and phosphorus fertilization on Weibei Plain is recognized to be of great significance for optimizing soil water and fertilizer management of wheat and achieving high crop yield and efficiency in rainfed areas. A five-year long allocation experiment was carried out to study the effects of soil moisture before sowing and phosphorus fertilization on the yield and water and fertilizer use efficiencies of winter wheat in Weibei tableland of Yangling, Shannxi, China. There were 4 phosphorus rates, P2O50, 50, 100 and 150 kg /ha on the basis of N 160 kg /ha. The results show that precipitation from July to September in summer is the key factor to decide SMBS on Weibei tableland, and they are linearly and positively correlated with 1 mm summer precipitation leading to an increase of 0.5 mm SMBS. For a stable or high wheat yield, the SMBS should be kept around 550 mm and summer precipitation around 380 mm. In years with adequate summer precipitation, the SMBS is not obviously decreased by the increased P fertilizer application in the previous winter wheat growing season. However, reasonable P application promotes the growth of winter wheat, and lead to more consumption of soil moisture during the growing season, then reduced soil moisture, and it is significantly decreased by 912 mm when the P2O5 rates is increased by each P2O5 50 kg /ha in the previous growing season in the years with little summer precipitation (less than 350 mm). In addition to soil moisture before sowing, adequate precipitation in the key growth stages is another important factor to ensure wheat yield in the areas. Calculation based on this experiment indicates that one mm of SMBS could produce 9.09.9 kg/ha of wheat grain, and one mm precipitation occurred in the key growth stages could lead to more grain yield as high as 28.633.3 kg/ha. Meanwhile, SMBS restricts the allocation and transportation of dry matter from vegetative parts to grain. For a higher winter wheat yield and water and fertilizer use efficiencies in the area, less P fertilizer is needed in the years with adequate SMBS, while more P fertilizer is needed when the SMBS is deficient.