In this article, L-ascorbic acid cellulose ester, a polymer with antioxidant properties, was synthesized using L- ascorbic acid and sodium carboxymethyl cellulose as feedstock. The whole reaction was divided into two parts: the preparation of carboxymethyl cellulose carbonyl chlorides and the synthesis of L-ascorbic acid cellulose ester. The optimal conditions of acyl chloride preparation: ratio (m/v) of CMCH to SOCl2 was 1:3, proportion(m/v) of CMCH to DMF was 1:20, reaction temperature was 110-120 degrees C, reaction time was 2h. The optimal conditions of L-ascorbic acid cellulose ester synthesis: ratio(m/v) of L-ascorbic acid to solvent was 1:3.5, proportion(Mol/Mol) of Carboxymethyl cellulose carbonyl chlorides to L-ascorbic acid was 1:1.3, reaction temperature was 20 C, reaction time was 22h. In this reaction conditions, the synthetic product not only saved the antioxidant activity of the groups, and added the safe and non-toxic ability of dietary fiber.