The long-chain alkyl quaternary ammonium hydroxide was synthesized by the hydrolysis and continuous ion membrane electrolysis of alkyltrimethylammonium methylcarbonate; and the alkyltrimethylammonium methylcarbonate was prepared by the reaction of alkyl tertiary amine and dimethyl carbonate. Take tetradecyltrimethylammonium hydroxide as an example, the influences of the electrolysis reaction temperature, current density, the concentration of anolyte and the discharging concentration of catholyte on the current efficiency of electrolysis reaction were investigated. And the optimized condition was: reaction temperature 65 ℃, current density 450 A/m2, the concentration of anolyte 1.4 mol/L, the discharging concentration of catholyte 0.15 mol/L. Under the optimized conditions, the current efficiency could reach 67%. The structure of the products were characterized by 1H-NMR and IR, the results showed that long-chain alkyl quaternary ammonium hydroxides were synthesized successfully. The surface activity, pH, wetting and foaming properties of long-chain alkyl quaternary ammonium hydroxides were measured.