An LED backlight module includes at least one LED and a light guide plate. The light guide plate includes a light incident surface, a light emitting surface connected to the light incident surface, and a bottom surface parallel to the light emitting surface. The at least one LED is placed on the light incident surface and spaced at regular intervals. The light from the at least one LED enters the light guide plate from the light incident surface and is reflected to the light emitting surface by the bottom surface. The light guide plate defines a plurality of concave dots on the bottom surface. The bottom surface is divided into a plurality of discontinuous dot zones. In the dot zone closest to the incident surface, proximity of the dot to the LED decreases the depth and the distribution density of the dots.