It can provide a theoretical basis for achieving optimal crop yields and minimal P losses to determine the critical soil P level and reasonable fertilization.Based on a 24year longterm fertilization experiment on ‘The national fertility and fertilizer efficiency monitoring base of loess soil in Yangling,Shaanxi province,longterm history data and the related analysis of soil were used to determine the critical value of soil OlsenP for crop yield and soil P leaching threshold by the Mitscherlich index model and the twosegment linear model respectively.The results showed that,the critical value of soil OlsenP was 26.2 mg/kg for winter wheat,and 13.9 mg/kg for summer maize.There existed an evident changepoint on soil OlsenP along with the increasing of soil total P,which was total P at 1.15 g/kg and OlsenP at 348 mg/kg,and the OlsenP increased greatly with the increasing of soil total P above the changepoint.Similar changepoint was found also between soil OlsenP and CaCl2P,the risk of P leaching increased greatly when OlsenP was above 39.3 mg/kg.Under the condition of no rotation,the application rates of phosphorus fertilizer(P2O5)were 80～95,60～80 and 10～15 kg/hm2 respectively,when soil OlsenP were＜25,25～40 and＞40 mg/kg for winter wheat.The application rates were 70～85,55～70 and 10～15 kg/hm2 respectively,when soil OlsenP were＜15,15～40 and＞40 mg/kg for summer maize.Under the condition of winter wheatsummer maize rotation,the application rates of phosphorus fertilizer(P2O5)were 100～120,90～100,80～90,and 15～20 kg/hm2 for winter wheat,and the application rates of phosphorus fertilizer(P2O5)were 50～60,45～50,25～40,and 5～10 kg/hm2 for summer maize,when soil OlsenP were ＜15,15～25,25～40 and ＞40 mg/kg,respectively.