Abstract: CO deep removal was investigated by combining preferential methanation and preferential oxidation(M-O method).In the M-O method,CO of about 1% in reformate from a water gas shift(WGS) reactor is reduced to about 0.1% in the first stage of preferential methanation,then further reduced to below 10×10^-6 in the second stage of preferential oxidation.The results show that in comparison of the M-M method(a method of CO deep removal with two-stage preferential methanation) the M-O method could be operated with a wider temperature range and a higher gas hourly space velocity at a lower temperature,and has almost the same thermal efficiency.In the other hand,although a reaction system of the M-M method is simpler,a reaction reactor of the M-O method could be more compact in comparison.In addition,a high-speed preferential oxidation step set at the outlet of the second stage in the M-M method or M-O method was proposed to remove CO to below 1×10^-6,which helps to enhance the stability of proton exchange membrane fuel cells under long time continuous running.