The invention provides a backlight module. The backlight module has a cavity, a reflecting cover, a light source and an auxiliary light-guiding diffusion structure. The cavity comprises a reflective surface, a mounting surface connected to the reflective surface, and a light-emitting surface connecting the reflective surface and the mounting surface; the light source a light-emitting diode, the reflecting cover mounted on the mounting surface, the light source being disposed inside the reflecting cover; the auxiliary light-guiding diffusion structure disposed on the reflective surface and able to assist in diffusing the light incident to the reflective surface to improve emission uniformity of the backlight module and display quality. Another object of the invention is to provide an LCD device, using backlight module having a single LED as light source and achieving brightness uniformity, improving display quality of the LCD device, reducing production cost of LCD device and increasing product competitiveness.