The invention belongs to the field of chemical industry, in particular relates to a method for preparing sodium carboxymethyl cellulose with a high degree of substitution, and aims to solve the technical problem about provision of the method for preparing the sodium carboxymethyl cellulose with the high degree of substitution. The method comprises the following steps: a, preparing ethyl alcohol and an aqueous solution of sodium hydroxide into a mixed solution; b, mixing the mixed solution of the step a, cellulose serving as a raw material, and solid sodium hydroxide uniformly to perform an alkalization reaction; c, adding an etherifying agent into the material which is obtained after the reaction of the step b to perform an etherifying reaction; d, adding the etherifying agent into the material after the reaction of the step c to perform the etherifying reaction again; e, preparing the ethyl alcohol and the aqueous solution of the sodium hydroxide into the mixed solution; f, mixing the mixed solution of the step e and the material after the reaction of the step d uniformly to perform the alkalization reaction again; g, performing post-processing. By the method, the sodium carboxymethyl cellulose with the high degree of substitution of over 1.35 can be prepared.