In order to study the influence of fiber content on the shear strength of sand-soil, we carried out direct shear tests on sand-soil reinforced with fiber of different fiber lengths, sand contents and fiber contents, and determined the levels of influential factors through single factor experiment. Furthermore, we employed response surface methodology to establish the regression equation of cohesion and analyzed the variance, and then verified the optimization scheme of response surface analysis. Results show that 1) fiber content has insignificant influence on internal friction angle of sand-soil reinforced with fiber, but has obvious influence on cohesion; 2) data simulated by the cohesion model are significantly correlated with test data, and the difference of lack of fit is not significant, indicating that the model is reliable; 3) the effect of sand content on cohesion is very significant, while the effects of fiber content and fiber length on cohesion is relatively significant, and insignificant, respectively; 4) the cohesion obtained from verification test shows little difference with the theoretical predicted value, which suggest that response surface methodology for theoretical analysis accords with the actual cohesion.