Abstract: Co-gasifying coal and natural gas is a new process based on methane steam reforming and coal gasification.Technological principle of synthesis gas preparation by co-gasifying coal and natural gas is illustrated. Experimental results indicated that the optimal outlet temperature of synthesis gas was 1000 ℃ and flame temperature declined obviously when O₂, H₂O(g) and CH₄ were feed into the gasification reactor at the same position.The concentration of CO and H₂ of synthesis gas obtained by theoretical calculation was more than 95%.Both the calculation and experimental results demonstrated that with the proper ratio of feed materials, this method can directly prepare synthesis gas with H₂/CO adjustable between 1.0 and 1.5.