Pot experiment was carried out to study the methods of determining available P content in the red soils under different tillage methods. The results showed that the contents of available P were different significantly extracted by different methods, and the content of available P determined by Olsen-method was the lowest. The correlation coefficients among the results of available P contents extracted by different methods reached extremely significant level. The correlation coefficients between the reference standards and available P contents extracted by different methods in pot experiments reached extremely significant level in upland soil and significant level in paddy soil. P uptakes by crop and available P contents extracted by Bray-method showed the best correlation, so Bray method is recommended for determining available P content in acid soils of southern China.