A backlight module includes a bezel and a reflective shell. The bezel includes a bezel base, a bezel side plate connected to the bezel base, and an engagement structure mounted on an external side surface of the bezel side plate. The reflective shell includes a reflective shell top plate and a reflective shell side plate, which is connected to the reflective shell top plate and has an engagement hole to be engaged with the engagement structure such that the reflective shell is tightly combined with the bezel.