The invention discloses a method for treating dye wastewater. According to the method, a multi-phase Fenton catalytic oxidation mode, namely a method for degrading the organic wastewater by catalytically oxidizing hydrogen peroxide with chlorine iron oxide, is adopted; the method is simple, mild in reaction conditions, high in speed and easy to operate, and well overcomes the defects of homogeneous Fenton oxidation, namely (1) consumption of a large quantity of acid is avoided because an acid condition is not required and the pH value is not required to be regulated in reaction; (2) Fe(OH)3 sediment is not formed in the reaction, and secondary pollution is not produced; (3) because the chlorine iron oxide is not dissolved in water and iron ions are not ionized in the water, the treated water is not yellow; (4) compared with similar Fenton oxidation, conditions such as ultraviolet, visible light, ultrasonic, microwave and electricity are not required to be introduced, and oxidative degradation can be performed in light-free reaction, so that waste of resources is avoided; and (5) due to multi-phase catalysis, the catalyst can be reclaimed and reused. The degradation rate reaches 99 percent in 10 minutes under the optimal conditions; and the method is an efficient and simple organic wastewater treatment method.