A simulation experiment device for biomethanation of carbon dioxide sequestered in coal seams comprises a biotransformation and circulation system, a bacterial community activity and metabolism environment monitoring system, a temperature regulation system and a methane producing effect evaluation and mechanism analysis system. The invention further discloses an experiment method for the simulation experiment device for biomethanation. The experiment method includes that with coal serving as a substrate and the carbon dioxide serving as a medium, bacterial communities producing the methane are cultured under suitable conditions, bacterial liquid is selected preferably, and carbon dioxide biomethanation effects are simulated indoors in terms of different temperatures, different coal ranks, different coal granularities, different carbon dioxide pressures, different bacterial community types and different metabolism environments so as to achieve the technology of biotransformation of carbon dioxide into the methane. The experiment method is easy in control of reaction conditions, and the simulation experiment device is compact in structure, low in cost and convenient to operate, thereby being of great scientific significance and practical value.