Abstract: The surface of Q235 iron with decarbonization treatment,and then oxidation-reduction pre-treatment is observed under SEM.It is exhibited that submicron crystal exists on the pre-treatment iron surface and the nanometer layer structure in the submicron crystal.After carburizing at 750℃ for different time in drop-feeding atmosphere carburizing furnace,rising temperature to 900℃ and keep 5 minutes then quencher,the micro-penetration hardness is detected,the microstru-cture is obsered under SEM & OM and the thickness of carburizing layer is measured.Resultsshow,that the pre-treatment of surface accelerate the carburize process obviously.