The present invention discloses a fluorescence method detection method of a phthalate plasticizer in a water-soluble material. The method comprises (1) hydrolysis; (2) synthesizing magnesium monoperoxyphthalate; (3) preparing a to-be-measured solution; (4) preparing a magnesium monoperoxyphthalate standard curve; 5) fluorescent derivatization; and (6) detection and conversion. According to the method, phthalate in a to-be-tested sample is converted into magnesium monoperoxyphthalate that can generate fluorescence, so that fluorescence detection of phthalates is implemented. Except a fluorospectro photometer, the phthalate plasticizer can be detected without a large-sized detection device, so that operation is convenient, costs are low, and detection conditions are moderate and controllable. The method is suitable for popularization and application in small and micro businesses.