A diffusion plate is made of a transparent body doped with diffusion particles. The transparent body comprises a first surface and a second surface opposite to the first surface. The first surface is provided with a plurality of micro grooves which are all of rectangular pyramid shapes. Every six adjacent micro grooves with a common connection point form a hexagram. The second surface is provided with a plurality of long strip arc grooves which are parallel to each other. The radius of arc in the long strip arc groove is defined as R, the center distance of adjacent long strip arc grooves 204 is defined as P, the maximum depth of each long strip arc groove 204 is defined as H, then R, P and H satisfy the following relation: 0.025mm<=P<=1.5mm, 0.01mm<=R<=2P, and 0.01mm<=H<=R. The diffusion plate can improve efficient utilization ratio of light and enjoy high uniformity of light emission. The invention also relates a backlight module adopting the diffusion plate.