Abstract: To study the process conditions of carboxymethylpachymaran (CMP) with high degree of substitution and its injection, using Poria cocos powder as raw material, the carboxymethyl reaction process conditions of CMP were optimized by orthogonal experiments. And CMP injection was prepared and tested by performance testing and pharmacology experiment. The results indicated that the obtained CMP had high degree of substitution, high purity and had carboxymethyl reaction characteristics. The optimal process condition for the carboxymethyl group substitution of pachyman was chloroacetic acid: sodium hydroxide=1.15:1, the reaction temperature 75℃, the reaction time 3 h. Under this optimal condition, the degree of carboxymethyl group substitution (DS) was 1.21. The CMP injection was stable, non-toxic, non-pyrogenic and non-irritating, so it was safe and reliable. The CMP could directly inhibit or kill tumor cells, enhance the phagocytosis of macrophages, regulate the immune function of the body. Preparation of CMP and its injection could help to enrich the product type of the polysaccharide, broaden the application scope and provide the early stage theoretical basis for the market investment.