Relationships between common methods of measuring soil available phosphorus and the actual total amount of available phosphorus (TAP) in soils were studied. TAP was obtained by planting crops successively until the crop was very insufficient in P. Olsen-P (P_ol) was estimated ar only 170/0 of TAP, and anion exchange resin P (P_ar) at about 42% of TAP. EDTA+NaHCO₃-P(P_e) and ATR mixed CER-P(P_mr) were poorfy correlated with TAP. The correlation coefficient tretween Cowell total P and TAP was 0.825, significant at 0.001 level. The correlative coefficient between Cowtll inorganic P(P_ci) and TAP was 0.772, significant at 0.01 level. The content of organic P which is available for crop in Cowell total P was abowt 24-33%. The effects of soil critical P buffering capacity (CBC), organic matter, and clay contents in soil were of great importance. CBC was obtained from the isotherm of P adsorption at equilibrium P concentratian of 0.1μg/g, which is better than the MBC (maximum buffering capacity), when analyzing TAP. TAP can be estimated accurately by measuring some soil parameters (incfuding Cowell total P) and using three-factor regression equation of which the decides) coefficient (r²) was above 80%, much higher than that of single-factor (cowell total P) equation.