The invention discloses a method for detecting nonmetallic impurities in powder metallurgy tool and mold steel. According to the method, a powder metallurgy tool and mold material button ingot is prepared by fully utilizing the characteristics of high energy and no pollution of an electron-beam melting furnace and combining the characteristic of low nonmetallic impurity content of the powder metallurgy tool and mold steel, an image is analyzed, and the button ingot is subsequently analyzed to detect the purity level of the steel. According to the method for detecting the nonmetallic impurities in the tool and mold steel, the problems of long time for detecting the nonmetallic impurities in the tool and mold steel, low efficiency, inaccuracy result analysis and the like of the conventional metallographic method are improved.