The invention discloses a polyhedral oligomeric silsesquioxane-based amphiphilic triblock copolymer and a preparation method thereof, and relates to a polymeric copolymer. The polyhedral oligomeric silsesquioxane-based amphiphilic triblock copolymer consists of a first block polymethylacryl acyloxypropyl POSS (polyhedral oligomeric silsesquioxane), a second block poly (tert-butyl acrylate-styrene) and a third block poly-4-vinylpyridine. Through a reversible addition-fragmentation chain transfer (RAFT) polymerization method, the polyhedral oligomeric silsesquioxane-based amphiphilic triblock copolymer is prepared by three steps. By the preparation method, the length ratio of amphiphilic blocks is good in controllability; the preparation method is easy; the product is novel in structure; and easy acidolysis of the tert-butyl acrylate can further functionalize the amphiphilic block copolymer.