The invention relates to a preparation method for a diffusion panel for an LED panel lamp, comprising steps of providing a motherboard substrate, arranging a double-layer masking layer on the front face of the motherboard substrate, manufacturing a needed etching window on the double-layer masking layer, performing longitudinal etching in order to obtain trenches inside the motherboard substrate, performing transverse etching to obtain a plurality of micro-convex structures of the motherboard, thinning the back of the motherboard substrate, performing cutting on the motherboard substrate in order to obtain the needed motherboard, loading the metal motherboard into an injection molding machine, utilizing the regular injection molding technology to prepare the diffusion panel similar with the optical disc, wherein a diffusion panel circular hole which goes through the diffusion panel is formed in the center of the diffusion panel and light guiding structures corresponding to the micro-convex structures of the motherboard are formed inside the diffusion panel. The invention is simple in technology, compatible with the semiconductor technology, and reliable in safety, and can guarantee the light emitting effect of the front side.