An extension bracket module is used for mounting an outer switch board of a computer system. The extension bracket module comprises a top plate and a panel perpendicular to each other. The top plate is levelly disposed and the outer switch board is configured facing downward and mounted onto a bottom surface of the top plate in parallel. An upper side of the panel is connected to a front edge of the top plate. Therefore, the deficit that the switch board in the prior art requires an extra longitudinal or transverse space of the computer system can be overcome through the design of the extension bracket module.