Abstract: Inorganic cementing materials（cement, lime, etc.） are often used as binder and curing agent in slope protection projects to improve the mechanical properties of soil, but the excessive use of inorganic materials brings great burden to the natural ecological environment. Sodium Carboxymethyl Cellulose（CMC） is an environment-friendly biopolymer with the same properties of improving soil structure and mechanical strength. In this study, the improvement effect and law of CMC on Silty clay were tested by adding CMC into the soil. The results show that adding CMC to the soil can effectively improve its shear strength. Compared with the two treatment methods of aqueous solution and dry powder mixing method, the strength of the modified soil after directly adding CMC dry powder can be improved. The effects of mixing amount of CMC, water content and curing time on the CMC modified soil were analyzed. When the content of CMC was 2% and the moisture content was controlled at 15%, the improvement of soil strength was the largest.