The invention discloses a synthetic method of dye intermediate 2,4-bi-(B-ethyl sulfuryl sulphate) phenylamine, comprising the following steps: step one, synthesis of B-chlorohydrin sulphate; step two, synthesis of 2,4-bisodium thiophenol aniline; step three, synthesis of 2,4-bi-B-ethyl sulfuryl sulphate; and step four, synthesis of synthesis of 2,4-bi-B-ethyl sulfuryl sulphate phenylamine: adding 400ml of methanol in a 1000ml flask, adding 50g of 2,4-bi-B-ethoxyl thioether sulphate phenylamine, adjusting pH (potential of hydrogen) to be 6.5-6.8 by using potassium hydroxide, heating to 68 DEG C, adding 0.42g of catalyst, dropping 44g of 35% hydrogen peroxide slowly, reflowing for 2 hours at the end of dropping, tracking by a chromatograph, at the end, adding water to bring out methanol, cooling and precipitating, thereby obtaining the product 2,4-bi-(B-ethyl sulfuryl sulphate) phenylamine, wherein the HPLC (high performance liquid chromatography) purity is equal to or greater than 95% and the amino content is equal to or greater than 90%. The synthetic method disclosed by the invention is not only low in cost but also wide in application scope.