A lens includes a main lens, a first light-diffusion capping layer and a second light-diffusion capping layer formed on the top of the main lens in sequence. The main lens includes a light incident surface and a light exit surface opposite to the light incident surface. The main lens defines a recess in the top thereof, and the recess is located at a central region of the light exit surface and recessed inwardly toward the light incident surface. The first and the second light-diffusion capping layers are received in the recess, and the second light-diffusion capping layer is located over the first light-diffusion capping layer. A refractive index of the first light-diffusion capping layer is smaller that that of the main lens but larger than that of the second light-diffusion capping layer. A backlight module source incorporating the lens and the LED light source is also provided.