This invention relates to a homogeneous method for preparing 1, 2, 4-acid in water-alcohol solvent. The method comprises: dissolving beta-naphthol with ethanol instead of liquid alkali, and performingnitration reaction, addition reaction and sulfonation reaction to obtain the product. The yield of 1,2,4-acid is up to 70-74%, the consumption of H2SO4 is reduced by nearly 1/3, the recovery rate ofethanol solvent is up to 80-85%, and the generation amount of wastetwaer is 1/2 that of alkali solvent method. The method has such advantages as adequate utilization of resources, high apparatus utility and low production cost. The method can be widely used to prepare 1, 2, 4-acid, an intermediate for producing naphthalene series dyes. The obtained 1,2,4-acid can be widely used to synthesize acidcomplex pink B, acid mordant black R, acid complex blue GGN and acid mordant bordeaux BN dyes and azo dyes.