(1S, 3R)-methyl 1-(4-(methoxycarbonyl)phenyl)-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole-3- carboxylate hydrochloride, the key intermediate of RSL3, was synthesized by an efficient and parctical method from D-Tryptophan through a two-step reaction, involving esterification and Pictet-Spengler reaction. The Pictet-Spengler reaction conditions were investigated, and the optimal conditions were as follows: the molar ratio of D-tryptophan methyl ester hydrochloride and methyl 4-formylbenzoate is 1:1.1, the mixture was stirred in acetonitrile and refluxing for 6 h. The trans-isomer (RSL3 intermediate) was obtained by suction filtration. The structures of intermediate and the product were confirmed by 1HNMR, 1H-1H NOESY and ESI-MS.