Based on the field test of saturated D-optimal designs with a匆uare,This paper deals with the response equa-tion of N and P fertilizer,on Spring Whest in three different yild ecosystem in Shanghuang experimental station.The mathmatic model of fertilization with different adaptability has been established,The main effect and mutualeffects of N and P fertilizer have been analized and the optimum of fertilizer required has been caculated according tothe model. fertilizer amount applied and the optimum ratio of N and P of crops grown in low terrace have been cacu-lated as an example.