Silica sol grout has advantages of good groutability, controllable gelation time, non-toxicity and high durability, however the compressive strength of silica sol grouted sand is relatively low, which restricts its application. In this paper, a series of single-factor tests were carried out to examine the effects of various factors on the compressive strength of grouted sand. Those factors include the type and concentration of gel-agent, the mass ratio of silica sol to gel-agent and the pH value of grout. In addition, response surface method was used to study the effect of the interaction of the factors including the concentration of gel-agent, the mass ratio of silica sol to gel-agent and the pH value of grout on the compressive strength of grouted sand. The experimental results demonstrate that the following factors are arranged in a descending order in terms of the influencing degree of a single factor, the concentration of gel-agent, the pH value of grout and the mass ratio of silica sol to gel-agent. Moreover, the following factors are arranged in a similar manner regarding interaction effects between two factors, interaction between gel-agent concentration and grout pH value, interaction between gel-agent concentration and the mass ratio of silica sol to gel-agent, and interaction between the mass ratio of silica sol to gel-agent and the pH value of grout. Based on response surface method, the optimized compressive strength of silica sol grouted sand can be achieved when the mass concentration of gel-agent, the mass ratio of silica sol to gel-agent and the pH value of grout are selected as 7%, 7∶1 and 7, respectively. The difference between predicted values of response surface method and experimental measurement is minor, suggesting that response surface method can be used to optimize the proportion of silica sol grout.