The fatty alkyl trimethyl ammonium oxalate was synthesized with Oxalic acid andalkyltrimethylammonium methylcarbonate, which was prepared by the reaction of alkyl tertiary amine and dimethyl carbonate (DMC). Take tetradecyltrimethylammonium oxalate as an example, the influences of reaction regents, reaction temperature, reaction time, the concentration of alkyl tertiary amine were investigated. And the optimized conditions were reaction at 150 ℃ in DMC for 3 h, the concentration ofalkyl tertiary amine 0.05 g/mL. Under the optimized conditions, the productivity could reach 85%. The structure of the products were characterized by means of 1HNMR, and the results showed that fatty alkyl trimethyl ammonium oxalates were synthesized successfully.