The invention relates to a method for preparing phosphorous detecting test paper, and belongs to the field of chemical analysis. The phosphorous test paper consists of filter paper impregnated with antimony potassium tartrate, ammonium molybdate and ascorbic acid. Each one square centimeter of the filter paper contains 0.01 to 0.02 mg of the antimony potassium tartrate, 0.04 to 0.07 mg of the ammonium molybdate and 0.04 to 0.07 mg of the ascorbic acid. The used filter paper can be qualitative filter paper, quantitative filter paper or chromatography filter paper. The reagent content of the phosphorous test paper is only a few tenths to hundredths of the using amount of the reagent in other phosphorous ion detecting method, so that the testing cost is reduced greatly. The test paper has the advantage of simple preparation, convenient operation, high sensitivity and particular suitability for field and site operation, and the content of phosphate ions of a sample can be judged by visually comparing the colors of the test paper which develops the color and a standard color card, so that the test can be performed by non-professional personnel. The reagents used in the invention are common chemical reagents, and are nontoxic, safe and reliable; and the test paper has wide application range, and can be used for measuring the phosphorous content of various phosphate fertilizers, soil, crop hydroponics nutrient solution, various phosphorous-containing solution and sewage.