Abstract: Disclosed are liquid vinyl functionalized cage-type polyhedral oligomeric silsesquioxane modified by low-molecular-weight polysiloxane and a preparation method thereof. Under the catalytic action of tris(pentafluorophenyl)borane, cage-type octakis (dimethylsiloxy)-T8-silsesquioxane and hetero telechelic polydimethylsiloxane undergo a Piers-Rubinsztajn reaction, to obtain liquid Vi-POSS. Side chains of the liquid vinyl functionalized POSS in the present disclosure are Si—O—Si chain links, have better heat stability than that of common long-carbon-chain side chains, and contain vinyl functional groups capable of participating in chemical reactions, which not only have good mechanical enhancement and heat resistance properties, but also have chemical reactivity.