In order to study the orbital angular momentum of higher-order diffraction beams, based on the method of computer generated holography, the perfect vortex beam with different diffraction orders is generated on the Fourier plane of space light modulator, and its topological charge is measured by spherical wave interferometry. Theoretical and experimental results show that the topological charge l of integer and fractional perfect vortex beams at different diffraction order p satisfies the relation of l=mp , where m is the topological charge of the phase mask. Furthermore, the optical vortex array with different diffraction order is also studied experimentally, the results show that the topological charge of optical vortices satisfies the relation of l=p , and the higher-order diffraction beam has greater orbital angular momentum than the diffraction beam at the +1 order. This study provides theoretical and experimental reference for further research and application of optical vortices and optical vortex arrays.