Treatment of printing and dyeing wastewater by the device of high gradient magnetic separation (HGMS) developed by author was tested. The results showed that printing and dyeing wastewater contained varied chemical composition and whose initial concentration of chromaticity and COD were 800 and 565mg/L respectively can be well cleaned by Fenton oxidation—magnetic seed coagulation—HGMS. The removal rate of chromaticity and COD was up to 92.6% and 79.5% respectively. The effluent can meet the national drainage criterion. The optimum technological parameters are as follows: pH=6, [FeSO4·7H2O]=250mg/L, [H2O2]=1.3ml/L, [PAM]=0.75 mg/L, dose of magnetic particle W=150mg/L,current intensity I=8A, current velocity U=2.420L/min, packing density of stainless steel wire R=1.00%-1.43%. Recovery rate of magnetic particle was up to 90% by regenerated technique of chemistry in combination with physics.