This invention provides a composite diffuser plate comprising a light-emitting layer for emitting light, a middle layer for guiding light, and a light-entering layer for entering light, being sequentially stacked downwardly. At least one surface of the middle layer is provided with an array of curved protrusions. Refractive indexes of the light-emitting layer, the middle layer and the light-entering layer are gradually increased. This invention further provides an ultra-thin direct type backlight module. In the composite diffuser plate of this invention, in addition to a gradual increase in refractive indexes of the light-emitting layer, the middle layer and the light-entering layer, the middle layer is provided with a microstructure having curved protrusions, which further enhances diverging effect of emitting angle. The direct-light TV can increase a light-emitting area with a small OD value, and thus improves a LED Mura problem, realizing a slim direct-light TV and enhancing market competitiveness.