A light source module includes a light guide plate (LGP), at least one light emitting element, a reflector, and a plurality of spacer units. The LGP has a first surface, a second surface opposite to the first surface, a light incident surface connecting the first surface and the second surface, and a plurality of optical microstructures. The light emitting element is located adjacent to the light incident surface. The reflector is adhered to the second surface through an adhesive gel. The spacer units are located between the LGP and the reflector, and sizes of the spacer units are larger than or equal to 1 micrometer. The adhesive gel includes a first adhesive gel and a second adhesive gel. The first adhesive gel is located between the spacer units and the LGP, and the second adhesive gel is located between the spacer units and the reflector.