A light source module adapted to provide a first illumination beam to a display apparatus is provided. The display apparatus includes a display panel for displaying a 2D/3D image. The light source module includes a first wedge-shaped light guide plate, a first light emitting device, a second light emitting device, and a light source driving module. The first wedge-shaped light guide plate has a first and second light incident surfaces and an optical grating pattern. The first light emitting device and the second light emitting device are respectively disposed beside the first light incident surface and the second light incident surface. In a 2D/3D image display mode, the light source driving module controls to turn on the first/second light emitting device for providing the first illumination beam to the first wedge-shaped light guide plate. A method for driving the display apparatus is also provided.