The finite element method is used to numerically simulate the grouting of microfractured rock mass, so as to study the coupling mechanism between grout and rock mass. And then the continuous formula is taken as the control formula for grout flow, and the modified Darcy′s law is used to describe the moving process of grout in fractured rock mass. Finally, based on elastic theory, the calculation method for grouting diffusion process in microfractured rock mass is proposed considering the effect of fluidsolid coupling, so as to study the influences of fracture opening and rock mass elastic modulus on grouting diffusion distance. The study results show that: (1) The fracture opening reduces from grouting hole surrounding to frontal surface of grout diffusion during grouting; and the calculation error of grouting pressure can be reduced by 30% and that of grouting diffusion radius can be reduced by 15% when considering the effect of fluidsolid coupling. (2) The influence of fluidsolid coupling on grouting diffusion should be fully considered during grouting design.