Effects of long-term fertilization on the relationship of alkaline phosphatase activity (APA) with phosphorus forms in loess hilly-gully region were studied by long-term fertilization experiment from 1988 to 2011. The results showed that compared with CK, the long-term fertilization of organic manure and chemical fertilizer could significantly increase APA. The correlations of APA were extremely significant with the content of Olsen-P, total organic phosphorus (T-OP), moderately labile organic phosphorus (ML-OP), moderately resistant organic phosphorus (MR-OP), Ca2-P and Ca8-P. The order of direct-effect of different phosphorous forms on APA was Ca8-P (-5.706 9) >Fe-P (4.180 5) >Ca2-P (2.760 4) >Ca10-P (0.980 0) >MR-OP (0.892 4) > Al-P (-0.567 5) >O-P (-0.294 4) >L-OP (labile organic phosphorus) (0.268 1) >ML-OP (0.210 3) >HR-OP (high resistant organic phosphorus) (-0.165 2).