【Objective】Soil Phosphorus Storage Capacity (SPSC) is an index developed on the basis of the degree of phosphorus saturation (DPS), and can be used to effectively assess and monitor the status and release potential of soil phosphorus storage. Therefore, based on a long-term (1988—) fertilization experiment in a field of upland red soil, this paper tracked variations of the SPSCs in the red soil and its various fractions of soil aggregates and discussed impacts of soil P input on the SPSCs.【Method】A total of 33 soil samples were collected from the surface soil layers of the 11 treatments of the experiment, i.e. NK, NPK, NP, PK, NPKCa NPKCaS, CK, PS (1/2NPK + peanut straw), RS (1/2NPK + rice straw), FR (1/2NPK + fresh radish) and PM (1/2NPK + pig manure), for fractionation into soil aggregates ( > 2 mm, 2.0 ~ 1.0 mm, 1.0 ~ 0.25 mm and 0.25 ~ 0.053 mm) with the wet-sieving method, analysis of SPSCs in the soil and aggregates, exploration of effects of P input on SPSC, discussion on relationships of SPSC with soil total phosphorus (TP) and available phosphorus (Bray-P). In the end, the risk of soil phosphorus loss was assessed and “safe life” of the soil continuing to accommodate exogenous phosphorus.【Result】Among the inorganic treatments, Treatment NK was the highest in SPSC, reaching up to 265 mg•kg^-1, which was 1.9, 1.6, 1.9, 2.0 and 2.4 times that respectively of treatment NPK, NP, PK, NPKCa and NPKCaS. The fractions of soil aggregates exhibited an high to low order of 1 ~ 0.25 mm, 0.053 ~ 0.25 mm, > 2 mm, 1 ~ 2 mm in rate of contribution to the soil total SPSC. So, based on the current phosphorus application rate, it was estimated that the upland of red soil might remain safe for 30 years. Among the combination treatments, Treatment PM displayed a negative value in SPSC, reaching up to -333 mg•kg^-1. In this case, P application should be stopped immediately or fertilizer application rate should be adjusted. Treatment PS, RS and FR remained to be positive in SPSC value and did not vary much between them and followed an high to low order of 1 ~ 0.25 mm, > 2 mm, 0.053 ~ 0.25 mm, 1 ~ 2 mm in SPSC contribution rate of soil aggregates. So based on the current phosphorus application rate, the soil under the treatments might remain safe for 41, 30 and 14 years, respectively. However, the soil under Treatment CK may remain safe for 51 years.【Conclusion】According to the correlation analysis of SPSC, TP and Bray-P, when SPSC stay exceed 10 mg•kg^-1, application of phosphorus in the upland of red soil upland is absolutely "safe"; if it is in the range of -10 mg•kg^-1 ~ 10 mg•kg^-1, phosphorus in the red soil is extremely unstable and extremely liable to get leached into the surroundings or water; when SPSC stay below -10 mg•kg^-1, urgently calls for immediate halt of P application and readjustment of fertilization schemes so as to lower the risk of P polluting the environment.