An electric-substituting natural gas combined system and process based on coal gasification and methanation are disclosed. The process is carried out by delivering oxygen, powdered coal or water-gas slurry into gasified apparatus, recovering for crude gasified gas by wet heat, delivering into sulfur-resisting carbon monoxide carbon reactor, adjusting hydrogen-carbon ratio, entering into desulfurizing decarbonizer, recovering elementary sulfur while enriching carbon dioxide, delivering synthetic gas into methane reactor to generate substituted natural gas as domestic gas partially, entering into gas and steam combined circulator partially, and entering into substituted natural gas storage tank partially. It integrates coal gasified, methanation and gas steam combined circulation together, it's efficient and clean, has better utilizing rate, no CO2 discharge and need for changing gas turbine or load.