Ammonium polyphosphate(APP)fertilizer has slow-release property and can provide long-term phosphorus supply in calcareous soils. However，the slow release may lead to insufficient phosphorus supply for crops in the seedling stage，which may affect the final yield. The aimed to explore the reasonable application rate of APP fertilizer for maize and its effect on the inorganic phosphorus fractions in fluvo-aquic soil，and to provide scientific basis for rational application of APP fertilizer. A pot experiment was conducted with six APP levels，namely P2O5 0，30，60，90，120 and 150 mg/kg. The biological indicators and phosphorus absorption and utilization of maize were determined，as well as the available phosphorus and inorganic phosphorus fractions in the soil. The Results showed that compared with the control，APP fertilizer significantly increased the plant height，stem diameter，aboveground and root dry weight of maize. The plant height，stem diameter and aboveground dry weight showed a trend of large increase in the range of 0-90 mg/kg and small increase in the range of 90-150 mg/kg. The plant height，stem diameter，stem and leaf biomass at the level of P150 were 71.0%，68.8%，334.5% and 201.6% higher than those of P0，respectively. The phosphorus content and phosphorus fertilizer utilization efficiency of maize stem and root were the lowest at the level of P90，but there was no significant difference in phosphorus fertilizer utilization efficiency among P120 and P150. The available phosphorus content in the non-rhizosphere soil showed a significant linear relationship with the application rate of APP fertilizer，and each 1 mg/kg APP application rate was equivalent to an increase of 0.0894 mg/kg of available phosphorus in the non-rhizosphere soil. The available phosphorus content in the rhizosphere and non-rhizosphere soils was still above 13.23 mg/kg after 70 days of phosphorus application. The total inorganic phosphorus in the soil increased with the increase of APP fertilizer application rate. Compared with P0，the contents of Ca2-P and Al-P showed significant changes，while the content and proportion of O-P showed no significant difference among the phosphorus application levels. The Ca10-P content at P150 was significantly higher than that of P90 and below，and the Ca10-P accumulation amount increased by 101.70 mg/kg compared with P0. Based on the results of this study，APP fertilizer could maintain a high level of available phosphorus in the rhizosphere and non-rhizosphere calcareous fluvo-aquic soil. The biomass accumulation of maize was insufficient at the level of P2O5 60 mg/kg and below，and the content and proportion of Ca10-P in the soil increased at the level of P2O5 120 mg/kg and above. P2O5 90 mg/kg is a suitable APP application rate for maize in fluvo-aquic soils.