Abstract: A comprehensive thermodynamic analysis was made on the carbon deposition behavior for the production of substitute natural gas (SNG) through syngas methanation. The component concentrations and the equilibrium constants of ten reactions involved in the syngas methanation were calculated at different temperatures; the effects of temperature, pressure, and the addition of other compounds in the feed gas on the behavior of carbon deposition were investigated. The results indicated that the catalyst bed is prone to carbon deposition at 550~800 ℃ and 0.1~1.5 MPa; as a result, lower temperature, higher pressure, and a larger H₂/CO ratio are suitable for the methanation reactions. The addition of steam in the feed gas may alleviate the carbon deposition to a large extent, whilst a large amount of CO₂ or CH₄ in feed gas may lead to carbon deposition.