A high-brightness diffusion plate with trapezoid lens applied to a direct-type backlight module is disclosed. The high-brightness diffusion plate with trapezoid lens according to the present invention consists of a diffusion plate and a plurality of trapezoid lens disposed on at least one side of the diffusion plate for improving light efficiency and diffusion effect of the diffusion plate. By the diffusion plate with trapezoid lens, the direct-type backlight module provides better light output as well as more uniform brightness. Moreover, the diffusion plate of the present invention is used in combination with all or part of optical film. The optical film includes brightness enhancement film (BEF), an upper diffuser sheet and an lower diffuser sheet. The diffusion plate is made from plastic. By extrusion, the diffusion plate and the plurality of trapezoid lens are easily processed to form an integral. Therefore, the direct-type backlight module has better light output efficiency with lower cost.