As a green, environmentally friendly, and cost-effective grouting material, geopolymer requires consideration of grouting performance indicators such as strength and fluidity in order to achieve good injectability. For this reason, indoor ratio optimization experiments were conducted using liquid-solid ratio, water glass content, and water glass modulus as experimental factors. A multivariate second-order response surface regression model was constructed for compressive strength, flowability, and final setting time, and the influences of single factor and its interaction on various grouting performance indicators were obtained through variance analysis. The degree of influence of experimental factors on grouting performance indicators is as follows: liquid-solid ratio, water glass content, and water glass modulus. The interaction between liquid-solid ratio and water glass content has a significant impact on compressive strength, while the interaction between the other two factors has no significant impact on grouting performance indicators. Using the analytic hierarchy process and expert assignment method to obtain the relative weights of various grouting performance indicators, a multi-objective satisfaction function was constructed to optimize the ratio of slag-fly ash geopolymer grouting materials. Based on this, SEM testing was conducted on the slurry stone body with the best comprehensive ratio of grouting performance indicators. The results show that a small number of spherical unreacted fly ash particles can still be observed in the system, the slag particles and cement particles are basically fully reacted, and the oligomeric gel-like reaction products are rearranged and extended by deposition, and cross-lap with each other to form a dense and complete spatial network-like structure.