[Objective] The effects of ryegrass growth on the physical properties and shear resistance of a mixed substrate were studied in order to provide a scientific basis for the rapid restoration of coal gangue hill vegetation and for the prevention of soil erosion. [Methods] The physical structure of gangue is poor and the nutrient content is low. Ryegrass was planted in pots to which phosphogypsum and mycorrhizal residue were added to determine the effect of ryegrass growth on the physical properties and shear resistance of a mixed substrate. [Results] ① The addition of different proportions of phosphogypsum and mycorrhizal slag significantly increased the growth of ryegrass. Height, aboveground dry biomass, root weight density, and chlorophyll content of ryegrass on the mixed coal gangue substrate consisting of 20% phosphogypsum and 10% mycorrhizal slag had the best effect, followed by the mixed substrate consisting of 10% phosphogypsum and 10% mycorrhizal slag. ② The addition of phosphogypsum and slag significantly increased the aeration and water-holding capacity of the gangue mixed substrate in which the natural water content, total porosity, capillary porosity, and non-capillary porosity of the gangue mixed substrate with 20% phosphogypsum and 10% slag were increased by 18.88%, 14.18%, 13.12%, and 18.08%, respectively, and the bulk density was decreased by 24.76% compared with the respective values observed for the gangue mixed substrate with only 10% slag. ③ The shear strength of the gangue mixed substrate with 20% phosphogypsum and 10% mycorrhizal slag increased by 71.71%, and the cohesion and internal friction angle increased by 102.84% and 45.05%, respectively, compared with the mixed substrate having only 10% mycorrhizal slag. [Conclusion] The coal gangue mixed substrate with ryegrass root complex having 20% phosphogypsum and 10% mycorrhizal residue had the greatest shear resistance and was beneficial for controlling soil erosion in coal gangue hills.