ABSTRACT The experiments on microwave pyrolysis of soybean straw are studied to produce hydrogen-rich gas under CO2 atmosphere in this paper. The microwave power has an important effect on the temperature. The final temperature increases and the time to obtain the highest temperature is shortened with the power increasing. The gas yield, H2 yield and potential H2 yield increase rapidly with the power increasing, and the gaseous yield at CO2 atmosphere is up to 55.70% at 1000 W, and it is higher than N2 atmosphere. The main components of microwave pyrolysis gas product are H2 and CO, the content of syngas (H2+ CO) at CO2 atmosphere is 84.19% at 1000 W, which is more than N2 atmosphere. However, H2/CO ratio is about 0.80 at CO2 atmosphere, which is lower than N2 atmosphere, and H2/CO ratio at CO2 atmosphere is not suitable for the requirements of chemical synthesis. If it is used to synthesize liquid fuels, H2/CO ratio must be adjusted.