NOVELTY - p-Hydroxyphenylacetic acid and carbonate are dissolved in solvent, reacted with p-methoxybenzyl chloride, crystallized, and dried to obtain intermediate (I). Intermediate (I) is dissolved in solvent, and small molecules of alcohol and carboxylic acid ester are dripped. The contents are reacted, extracted, crystallized and dried to obtain intermediate (II). Small molecules are dripped in intermediate (II), and intermediate (II) is oxidized, crystallized, filtered, and dried to obtain 2-(4-(4-methoxy-benzyloxy)-phenyl)-malonic acid mono-(4-methoxy-benzyl) ester.    USE - Preparation of 2-(4-(4-methoxy-benzyloxy)-phenyl)-malonic acid mono-(4-methoxy-benzyl) ester (claimed).    ADVANTAGE - The method enables uses less than 10 raw materials and agents for reaction, is easy to control, simple (only 3 reaction steps are involved), and economical, enables large-scale production, and uses aprotic solvent with low boiling point, thus reducing energy consumption of distillation process. The aprotic solvent can be easily recovered and recycled, and controlled conveniently.    DETAILED DESCRIPTION - 304 g p-Hydroxyphenylacetic acid and 640 g carbonate are dissolved in 2000 ml aprotic solvent, heated for 30 minutes at 50?o C, and 727 g p-methoxybenzyl chloride is added and reacted at 60-100?o C, preferably 72?o C, for 8-10 hours, preferably 8 hours. Reaction is detected by thin-layer chromatography. The reaction mixture is cooled to room temperature, added to 5000 ml ice water, stirred, crystallized, filtered, water-washed twice, dried, recrystallized using 5460 g anhydrous ethanol, cool-crystallized, filtered, and dried to obtain 740 g (4-(4-methoxy-benzyloxy)-phenyl)-acetic acid 4-methoxy-benzyl ester (intermediate I) with a yield of 99.5%. The weight ratio of p-hydroxyphenylacetic acid, p-methoxybenzyl chloride, and carbonate is 1:2.07-3.1:1.39-3.63. Intermediate (I) is dissolved in 2650 ml toluene and 298 g alcohol, and 331 ml small molecules consisting of alcohol and carboxylic acid ester are dripped over 1 hour. After addition completion, reaction is carried out at 0-60?o C, preferably 15-20?o C, for 10-12 hours, preferably 12 hours. The reaction mixture is added with 934 ml water, stirred, and layered. The organic layer is washed twice with 934 ml water, the water layer is combined, pH-adjusted to 2-3 using 6 mol/L hydrochloric acid, cooled, crystallized, filtered, and dried to obtain 783 g 2-(4-(4-methoxy-benzyloxy)-phenyl)-3-oxo-propionic acid 4-methoxy-benzyl ester (intermediate II) as pale yellow solid. 0.43 ml small molecules consisting of alcohol and carboxylic acid ester are dripped with respect to 1 g of intermediate (II). Intermediate (II) is dissolved in 17830 ml methanol and 1018 ml/1 g intermediate oxidant is dripped in 1-2 hours, preferably 2 hours. The contents are heat-refluxed for 4-6 hours, preferably 4 hours, while stirring. 3915 ml Water is added, and the reaction mixture is concentrated under reduced pressure, crystallized, filtered, washed, and dried to 734 g obtain 2-(4-(4-methoxy-benzyloxy)-phenyl)-malonic acid mono-(4-methoxy-benzyl) ester. The crude product is crystallized using petroleum ether/ethyl acetate mixed solvent to obtain 685 g pure product with a yield of 99.2%.