The wool was pretreated with Fenton reagent in this paper, on this basis, 4-hydroxy benzaldehyde and concentrated nitric acid were used to discuss the dye-free coloration deeply. It was analyzed comparatively through a series of experiments on the wool before and after Fenton reagent pretreatment, and the effects of concentrations, temperature and time on the coloration were further discussed. The experiment indicated that, compared with untreated wool, the color of wool with Fenton reagent pretreatment was deeper and the coloration rate was quicker. It realized good coloration at lower temperatures, which achieved the goal of saving energy and emission reduction. The optimal conditions were that concentrations of 4-hydroxy benzaldehyde and concentrated nitric acid were 2.5% and 3% respectively, reacting time was 90min, and reacting temperature was 70°C.