The invention discloses a detection method for detecting organophosphate flame retardants in ABS plastic. The detection method at least comprises the following steps of 1 sample pretreating, wherein a to-be-detected sample is accurately weighed, crushed and dissolved, a hydrolytic agent-acetate solution is added, oscillating is conducted for 0.5 h to 2 h at room temperature, filtering is conducted, a to-be-detected sample solution is obtained, and a chitosan-cerium (IV) complex is adopted as the hydrolytic agent; 2 sample detecting, wherein the to-be-detected solution is detected with a gas chromatography-mass spectrometer, and qualitative and quantitative preliminary analysis is conducted on the to-be-detected solution; 3 sample re-detecting, wherein the to-be-detected solution is detected with 31P-NMP, and further qualitative and quantitative analysis is conducted on a result by combining an analysis result obtained in the step 2. According to the method, the organophosphate flame retardants in the ABS plastic can be quickly, conveniently and accurately detected.