A moving bed was used as the reactor in experiments to produce synthesis gas by coal and natural gas co-conversion process. The effects of coal types on the temperature in the flame zone, the ingredients and the H-2/CO ratio of synthesis gas, together with the methane and steam conversions were investigated by using coke, anthracite, lean and fat coals as the raw materials. By comparing the results between coals and coke, it can be seen that the temperatures in the flame zone and the content of the active compounds (H-2, CO) of coals are higher than those of coke. In addition, the H-2/CO ratio of synthesis gas closes to the calculated value by thermodynamic equilibrium. For the produced crude synthesis gas with coals by coal and natural gas co-conversion process, in which the H-2/CO ratio varies in 1.0-2.0, the content of the active compounds (H-2, CO) is more than 92%, and the residual methane is less than 2%, the methane and steam conversion rates are more than 90% and 75%, respectively. All these results demonstrated that the concept of coal and natural gas co-conversion process is positive and feasible. (C) 2006 Elsevier B.V. All rights reserved.