A light source module and a LGP are provided, the light source module includes the LGP, a light source and an optical film. The LGP includes a bottom surface, a light-emitting surface, a light incident surface and a reflection surface. A projection of the reflection surface on the light-emitting surface has an arc shape. The optical film is disposed on the light-emitting surface, and includes a plurality of prism columns in arrangement. The bottom surface has a plurality of microstructures, and each microstructure has a first surface and a second surface. The first surface is closer to the light incident surface compared to the second surface, and an included angle between the first surface and the bottom surface ranges between 1 and 10 degrees. The light source module of the invention effectively narrows horizontal and vertical viewing angles, and light and slim tendency of the light source module is satisfied.