Selecting method for light guide plate of backlight module

A selecting method for a light guide plate of a backlight module comprises the following steps: S201 calculating a plurality of light diffusion effect indexes (M1) to respectively correspond to the light diffusion states of a plurality of first type light guide plates (100a, 100b); S203 defining a plurality of membrane frameworks (210) each of which corresponds to each light diffusion effect index (M1) so as to establish a corresponding database among the plurality of the light diffusion effect indexes (M1) of the first type light guide plates (100a,100b) and the plurality of the membrane frameworks (210); and S205 selecting one membrane framework (210) and the corresponding light diffusion effect index (M1) from the corresponding database so as to determine a critical node size (212) of a second type light guide plate (207) under the selected membrane framework (210). The selecting method can assure that the specific light guide plates and the specific membrane frameworks will not generate light diffusing after being arranged, thereby saving the development time, the manual labor and the production cost of the backlight module.