An embodiment of the invention provides a method of semiquantitatively measuring free fatty acids in edible oil; the method comprises (1) extracting free fatty acids in edible oil via an extracting agent to obtain extract containing free fatty acids to be measured, wherein the volume of the extracting agent is equal to that of the edible oil; (2) taking the extract of specific volume to be measured, adding nano gold solution and cationic polymer solution in the extract, and mixing well until the color never changes to obtain a colorimetric system to be measured; (3) comparing the color of the colorimetric system to be measured to that of standard colorimetric system to determine the content range of free fatty acids in edible oil. The method provided by the embodiment has the advantages that the analytic time is short, semiquantitative analysis can be finished within minutes, and the detection speed is higher than that of a titration method; as little organic solvents are used, the method is green.