In the present paper, light catalysis oxidation degradation of Malachite Green by Photo-Fenton reagent was researched. The influences of various parameters such as the wave length-absorbency curve of Malachite Green, the concentration-absorbency curve of Malachite Green, initial pH, optimum dosage of Fe2+, optimum dosage of H2O2, different light sources and cation-exchange resin, on dye degradation were researched. Through numerous experiments, the optimum condition for Malachite Green degradation was given. Under the optimal conditions, the sun light can promote this reaction apparently and the reaction time can greatly be shortened too. After the cation-exchange resin was introduced into Fenton system, the activation of Fenton reagent for degradation reaction was enhanced to a great extent, and the degradation effect of Malachite Green was better.