The most widely used method for determination of available phosphorous（P）in neutral，calcareous and alkaline soils was Olsen method. It was cumbersome operation by using activated carbon to remove organic matter color and indicator （2，4-Nitrophenol or p-nitrophenolic acid）to adjust acidity. In this study，available P of two national certified standard soils and agricultural topsoil samples of fifteen different soil types chose from northern and northwestern China were determined by Olsen method，base on molybdenum blue-ascorbic acid，in which contained 5.5 mol/L（H⁺ ）H₂SO₄， 10 g/L ammonium molybdate，0.5 g/L potassium antimony tartrate and 15 g/L ascorbic acid. Adding organic matter（humic acid）and adjusting acidity had little effect on the result of P standard curve，and on the basis of this，the experiments were conducted to investigate the influences of whether adding AC0 and adjusting acidity on the results of measuring Olsen-P in soil samples. The results demonstrated that whether using AC0 to remove organic matter color and indicator to adjust the acidity of solution had no influence on the measurement results of Olsen-P with soil organic matter content below 45.6 g/kg and pH range of 6.69-9.07. The relative error was between -10.9%-8.3%，and had a good relationship（y=1.0006x，R² =0.9994）with the conventional method. So organic matter and pH of soils had no significant effect on the measurement results of Olsen-P，and which as interference factors were eliminated. It simultaneously showed Olsen-P method was optimized with convenient and environmentally friendly，and could better meet the requirements of agriculture and other industries for determination of soil available phosphorus.