The quizalofop-p-ethyl is the high-quality product obtained by removing inactive optical isomers (L-body) in the process of synthesizing quizalofop-ethyl. Its mechanism is that the product is absorbed by stems and  leaves of weed and then bi-directionally transferred upward and downward in the bodies of plants, it is accumulated at both ends and in generating tissues between both ends to inhibit synthesis of fatty acid of cells. The quizalofop-p-ethyl is a kind of high-speed selective upland field stem leaf treating agent, has high selectivity between gramineous weed and dicotyldonous crop, is hardly affected by ambient conditions of rain water, temperature, moisture, etc., and has better effect of preventing gramineous weed of soybean fields.