Disclosed is a calculation method for a concrete crack chemical grouting grout diffusion radius. The diffusion radius of grouting grout is calculated under the effect of different grouting pressures according to the formula specified in the description; the influence of the crack width on the diffusion radius of grouting grout is calculated; the influence of crack chemical grouting duration time on the grout diffusion distance is calculated; the influence of the grouting grout viscosity on the grout diffusion radius is calculated. According to the calculation method for the concrete crack chemical grouting grout diffusion radius, calculation is easy, the technology is reliable, application is convenient, the requirement for engineering is met, and good economic benefits are reflected.