Lonidamine was synthesized from phenylhydrazine and 2,4-dichlorobenzyl bromide as the raw materials. Phenylhydrazine was acetylated, and then reacted with hydroxylamine hydrochloride, chloral hydrate and sodium sulphate to form N-acetyla-minoisonitrosoacetanilide, which was subsequently hydrolyzed to obtain 1H-indazole-3-carboxylic acid after Beckmann rearrangement and ring shrinking reaction. 2,4-dichlorobenzyl bromide was prepared by 2,4-dichlorotoluene and NBS with AIBN as catalyst, and then reacted further with 1H-indazole-3-carboxylic acid to get the product of lonidamine. The influence of process conditions on the yield of N-acetyla-minoisonitrosoacetanilide was studied by single-factor experiment and orthogonal test. The optimal conditions for the reaction were: the molar ratio of n(N-acetylphenylhydrazine), n(chloral hydrate) and n(sodium sulphate) 1:1.3:8.5, reaction temperature 90℃ and reaction time 13min. The process can get the product in 86.9% yield under the above optimized reaction conditions. The total yield of lonidamine was 31.2%. Structure of product was characterized by IR, 1H NMR and MS.