The invention discloses a method for generating a vortex light beam by use of a calculation hologram. The steps comprise: (1), utilizing a monocyclic Laguerre-Gaussian (LG) vortex light beam in a source plane (z=0m) coordinate system; (2), performing conjugate symmetrical extension on the complex amplitude of the vortex light beam, and obtaining symmetrical vortex light beam complex amplitude distribution; (3), performing Fourier transformation on the conjugate symmetrical vortex light beam complex amplitude distribution to obtain two-dimensional discrete real function distribution, performing DC component inhibition on real functions, and coding to form the vortex light beam calculation hologram; (4), performing Fourier inverse transformation on the calculation hologram, obtaining the light intensity distribution and the phase distribution of the vortex light beam, and taking the left half portions of the light intensity distribution and the phase distribution as the vortex light beam for digital reconstruction; and (5), loading the vortex light beam calculation hologram on a spatial light modulator, modulating incident laser and reconstructing the vortex light beam in a photoelectric mode. The method employs a conjugate symmetrical extension Fourier calculation holographic algorithm, the algorithm is rapid and simple, the calculation efficiency is high, and sidelobe-free high-quality vortex light beams can be generated.