Coal/char catalytic hydrogasification (CCHG) is a direct method to produce CH4 (synthetic natural gas, SNG). CaO has been studied as a promoter of transition metal compound catalysts for this process for decades. Our earlier work indicated that CaO alone has a high catalytic activity in CCHG as long as the temperature is higher than 750 degrees C and the Ca loading is higher than 0.42 mmol/ (g of char). Our recent work and literature review indicate that the high activity of CaO may be related to the iron in ash of the char used, and the threshold loading of CaO may be attributed to the presence of sulfur in the char. This work aims to address these issues particularly on synergetic catalysis of Fe-CaO and transformation of Fe-CaO-S during the hydrogasification. All the hydrogasification experiments were performed in a fixed-bed reactor at 800 degrees C and under a H-2 pressure of 1.5 MPa. Results indicate that both CaO alone and metallic Fe alone have little catalytic activity, but interaction of them yields a high activity. In this sense, CaO is not a catalyst promoter reported in the literature but a crucial catalytic component. The amount of Fe to fully excite the catalysis of 0.710 mmol of CaO is around 0.170 mmol, while the amount of CaO to fully excite the catalysis of 0.084 mmol of Fe is around 0.310 mmol. To yield a high catalytic activity, the optimum CaO/Fe molar ratio is around 4.0. The synergetic catalysis of Fe-CaO transforms from the CaO-dominate sites to Fe-dominate sites during hydrogasification, possibly due to differences in diffusion of Fe and CaO.