NOVELTY - Preparation of 2-(N-4-fluorobenzyl) methoxy-acetyl-amino methyl isobutyrate (I) comprises mixing 4-fluorobenzyl aminoacetic acid methyl ester (II) with N,N-dimethylformamide and e.g. tetraethyl ammonium bromide to obtain electrolyte, placing in an electrolytic cell, passing carbon dioxide to the cell, mixing the electrolyzed liquid with potassium carbonate and methyl iodide, adding hydrochloric acid, extracting the liquid and methylene dichloride, combining the organic layers, dewatering, filtering, decompression distilling the filtrate, removing methylene dichloride, separating and purifying.    USE - Synthesis of methyl-2-(N-4-fluorobenzyl)methoxyacetamino isobutyrate used for pharmaceuticals.    ADVANTAGE - The method efficiently and economically provides methyl-2-(N-4-fluorobenzyl)methoxyacetamino isobutyrate using simple process without causing pollution to environment.    DETAILED DESCRIPTION - Preparation of 2-(N-4-fluorobenzyl) methoxy-acetyl-amino methyl isobutyrate (I) comprises;    a) mixing 4-fluoro benzyl aminoacetic acid methyl ester (II) with N,N-dimethylformamide and tetraethyl ammonium bromide, tetraethyl ammonium iodide, tetraethyl ammonium chloride or tetrabutyl ammonium bromide in a mole ratio of 1:129:1 to obtain electrolyte, placing in a chamber type electrolytic cell with a stainless steel cathode and magnesium rod anode;    b) passing carbon dioxide to the electrolytic cell until it is saturated, conducting the carboxylation reaction with a constant current density of 1.5-5.0 mA/cm2 at 20-28 degrees C and electrification amount of 2.0 F per mole of compound (II), where F is the Faraday constant;    c) mixing the electrolyzed liquid with anhydrous potassium carbonate and methyl iodide in a mass ratio of 100 ml: 3 g: 3 ml at 55-65 degrees C, stirring and refluxing for 5 hours, adding hydrochloric acid to make the liquid have pH 7;    d) extracting the liquid and methylene dichloride in a volume ratio of 1:1, combining the organic layers, dewatering with anhydrous magnesium sulphate, filtering, decompression distilling the filtrate, removing the methylene dichloride, separating with a filtering column comprising petroleum ether, ether and methylene dichloride in a volume ratio of 20:1:1 and purifying to obtain compound (I), where the decompressing and rotary steaming temperature is 35 degrees C and the pressure is 0.1MPa.