The patent application relates to a fixed structure of modularized light guide plate and a backlight module, wherein the fixed structure includes a back board, a display panel, a light source, an optical module arranged between the back board and the display panel for receiving the light of the light source, and an aluminum extrusion. The aluminum extrusion is located on the upper part of the back board and is fixed on the back board. The optical module is clamped and fixed on the aluminum extrusion. By setting a clamping mechanism between the optical module and the aluminum extrusion, wherein the optical module is arranged between the back board and the display panel for receiving the light of the light source, the patent application realizes the limiting in Z-axis direction for the optical module in order to limit the movement of the optical module, prevents the optical module from being drooped and deformed due to its own weight when the liquid crystal display is inverted, and from colliding the other components in the backlight module and damaging the backlight module. Meanwhile, the ultrathin design is beneficial for guaranteeing the light incidence surface of the light source aligned with the light emission surface thereof centrally and avoiding light lose.