Based on the standard LY/T 12322015 forest soil phosphorus determination，through multiple experimental comparison，the determination of soil total phosphorus with acid soluble method was optimized.In the original method，DNT was used as indicator，and 2 mol/L sodium hydroxide solution and 0.5 mol/L sulfuric acid solution were used for color mixing，the color was from yellow to pale yellow，the color change was not obvious，and the naked eye judgment error was great.Optimized method used sulfuric acidsoluble perchlorate acid as digestion solution，and phenolphthalein as indicator，and used 4 mol/L sodium hydroxide solution and 0.5 mol/L sulfuric acid solution for color mixing，the color showed from red to colorless，which was more clear to distinguish，and the result was more reliable.