The invention relates to an electroreduction preparation method of 2-amino-5-methoxybenzoic acid derivatives represented by a formula I shown in the specification. A preparation reaction is shown in the specification, wherein n is selected from 1, 2 or 3; R is selected from hydrogen, methyl, ethyl or benzyl; Y is selected from C6H5, HO, Cl, Br, mesyloxy, p-toluenesulfonyloxy or M is selected fromCH or N; and W is selected from CH2, O, S, NH, HOCH, BocN, MeN, EtN, C6H5N, 4-ClC6H4N or 4-HOC6H4N. The electroreduction preparation method for the 2-amino-5-methoxybenzoic acid derivatives represented by the formula provided by the invention is characterized by comprising the step of performing constant-current or constant-voltage electrolysis in a diaphragm electrolytic cell by using an acid solution of a 5-methoxy-2-nitrobenzoic acid derivative as a catholyte and an acidic solution as an anolyte, wherein the voltage of a cathode working electrode is 1.00-2.50 V relative to that of a reference electrode, the current density of constant-current electrolysis is 25.0-250.0 mA/cm<2>, and the electrolysis temperature is 15-80 DEG C.