The invention provides a preparation method of 8-nitro-1,2,3,4-tetrahydroisoquinoline. The method comprises the steps that a, isoquinoline and a brominating agent are subjected to a bromination reaction in a strong acid solution to obtain 5-bromine-isoquinoline; b, nitrate and the 5-bromine-isoquinoline obtained in the step a are subjected to a nitration reaction in concentrated sulfuric acid to obtain 8-nitro-5-bromine-isoquinoline; c, on the condition that hydrogen is introduced, the 8-nitro-5-bromine-isoquinoline obtained in the step b is subjected to a catalytic hydrogenation debromination reaction in a solvent under the effect of a catalyst to obtain 8-nitro-isquinoline; d, the 8-nitro-isquinoline obtained in the step c is subjected to a reduction reaction in acetic acid under the effect of sodium borohydride to obtain the 8-nitro-1,2,3,4-tetrahydroisoquinoline. Compared with the prior art, bromine is used for positioning 5-C of isoquinoline, the follow-up nitration reaction is performed only on 8-C, then, the catalytic hydrogenation debromination reaction and the reduction reaction producing few impurities are performed in sequence, and the yield of the obtained 8-nitro-1,2,3,4-tetrahydroisoquinoline is high.