The invention belongs to the technical field of the preparation of medical stents, and specifically relates to a triblock copolymer and a porous lamellar stent and a preparation method thereof. The preparation method of the triblock copolymer comprises the following steps: 1) taking 1,4-butanedioic acid and 1,4-butanediol as reaction monomer to obtain a series of hydroxyl-terminated PBS prepolymers with different molecular weights by use of esterification reaction and melt phase polycondensation reaction; 2) taking MPEG as the raw material to obtain the MPEG-COOH through the esterification reaction, continuously acidating to obtain the MPEG-COCl; and 3) synthesis of the triblock copolymer: polymerizing the HO-PBS-OH and the MPEG-COCl to obtain the triblock copolymer. The synthesized triblock copolymer has higher molecular weight, better mechanical strength, better hydrophilic-hydrophobic balance and biodegradability, and satisfies the normal use conditions as the medical stent material.