The invention discloses a digital imaging technology-based method for calculating relative permeability of tight core, comprising the following steps: step S1: preparing a small column sample of tight core satisfying resolution requirements; step S2: scanning the sample by MicroCT-400 and establish a digital core; step S3: performing statistical analysis on parameters reflecting the characteristics of rock pore structure and shape according to the digital core; step S4: calculating tortuosity fractal dimension DT and porosity fractal dimension Df by a 3D image fractal box dimension algorithm; step S5: performing statistical analysis on maximum pore equivalent diameter λmax and minimum pore equivalent diameter λmin by a label. The present invention solves the problems of time consumption of experiment, instrument accuracy, incapability of repeated calculation simulations and resource waste by repeated physical experiment.