The invention discloses a method for calculating crack anisotropism gradient. The method comprises: based on acquired seismic data, obtaining angle information of pre-stack azimuth gather; based on the angle information, performing superposition processing on the pre-stack azimuth gather, to obtain corresponding post-stack azimuth seismic data cube; performing sparse pulse inversion on the post-stack azimuth seismic data volume, to obtain corresponding reflection coefficient body; based on a simplified Ruger HTI medium longitudinal wave approximate reflection coefficient equation, processing the reflection coefficient body and the angle information, to obtain a longitudinal wave variable coefficient difference value of the upper layer and the lower layer of a HTI medium and correlated variables; and based on the longitudinal wave variable coefficient difference value of the upper layer and the lower layer of the HTI medium and the correlated variables, calculating the anisotropism gradient. The method is based on post-stack azimuth data, and the high-quality part of the seismic data is selected to be used as inversion input data, thereby preventing direct influence of post-stack azimuth data on calculation results. The inversion method is high in stability and high in signal to noise ratio.