An exemplary backlight module (100) includes a diffusion sheet (110), a plurality of light sources (120), a plurality of supporting posts (130), a plurality of fasteners (140), and a reflective plate (150). The supporting posts are disposed generally between the reflective plate and the diffusion sheet to form a gap with a predetermined distance between the reflective plate and the diffusion sheet. The fasteners are engaged with the reflective plate and hold the light sources to mount the light sources in the gap above the reflective plate. The reflective plate comprises a plurality of elongate bumps (151), and the bumps face toward the diffusion sheet. Each bump is located midway between two adjacent light sources for concentrating and guiding reflected light beams toward a corresponding area of the diffusion sheet above the bump.