The present invention relates to the field of display technologies and discloses a diffusion plate, a backlight module and a display device. The diffusion plate comprises a main body structure. An accommodating slot for accommodating a light source assembly is formed within the main body structure, a support surface for supporting a display panel is formed on the surface of a side of the bottom wall of the accommodating slot which faces outside of the slot, and the accommodating slot is provided with a fixing portion for fixing the light source assembly. The above diffusion plate not only diffuses the light emitted by the light source assembly homogeneously, but also enables mounting and supporting of the light source assembly and the display panel. Moreover, the backlight module of the diffusion plate omits the structures such as a support backboard and a rubber frame, and further achieves structure simplification. Thus, the backlight module of the diffusion plate has good structural stability.