A method and a structure for improving the uniformity of light emitted from a backlight module are provided. In accordance with the present invention, a plurality of optical microstructures are intermittently distributed on an LGP of a backlight module. Each of the microstructures further includes a plurality of optical sub-microstructures. The optical microstructures and the optical sub-microstructures are distributed on the LGP with varied distribution intensities in three dimensions, such that at where the optical microstructures and the optical sub-microstructures are distributed with a larger distribution intensities the LGP refracts and reflects more light, and at where the optical microstructures and the optical sub-microstructures are distributed with a smaller distribution intensities the LGP refracts and reflects less light. In such a way, by designing particular distribution intensities of the optical microstructures and the optical sub-microstructures, the light emitted from the LGP can be uniformed.