The invention discloses a method for extracting fatty acid through a waste grease enzyme method. The method includes the following steps that firstly, waste grease without impurities is heated and stirred, activated white clay serves as a decoloring and deodorizing agent, normal-pressure decoloring is adopted, when the waste grease is decolorized, odor, part of metal ions, soap grains, colloid and impurities can be removed, and quality requirements of the waste grease for enzymolysis are met; secondly, the decolorized and deodorized grease is washed with water, water and impurities are removed, and neutral purified grease is obtained; thirdly, the neutral purified grease and composite lipase are mixed for hydrolysis reaction, and a hydrolysis mixed product is obtained; fourthly, the hydrolysis mixed product is separated to obtain upper-layer oil phase substances in a separation tank, distillation is continuously conducted after water washing to obtain mixed fatty acid, and the product is obtained. The method has the advantages of being low in energy consumption, little in equipment investment, simple in process, easy and convenient to operate, low in processing cost and the like, is suitable for production on different scales, facilitates resource development and utilization of kitchen waste grease, reduces environment pollution and improves work conditions.