Diffraction and grating are important contents of basic optical courses and optical experimentsplaying an important role and application in traditional optical technology and frontier scientific research.Byusing the spatial light modulator( SLM) , the experiment of fractional optical vortex based on the diffractioneffect of the fork grating is designed and caried out.The fork grating holograms are calculated by the computerprogram and loaded onto the SLM. The fractional optical vortex is generated and observed experimentally , and the characteristics and intensity distribution of which are also analyzed.Through this experiment ,students havefurther deepened their understanding of difraction and grating characteristics, stimulated their interest infrontier optical research and exploration, expanded their professional knowledge , and enhanced their innovativeawareness on optical research and control of light field.