Relationship between total phosphorus (TP) and available phosphorus (P) in a red soil under a long-term fertilization experiment beginning from 1988, was discussed through statistical analysis of its historical data. At the same time, sequential Olsen-P extraction was carried out to examine sustained P supply capacity in the red soil. Results show that the content of available soil P was a direct indicator of P fertility in the red soil and increased with the accumulation of TP; the supply levels of TP and available P in the red soil were determined by the amount of P surplus. According to the findings, the P content in the soil is adequate to meet the P need of at least 3~4 crops, if P fertilization decreases or ceases now. Consequently a new fertilization system should be worked out by taking into account both the agricultural effects and environment safety of soil P, to further rationalize the use of P resources.