Ram-type blow out preventer is important equipment used in oil drilling operations. Variable bore ram-type blowout preventer, as a improved type, is capable of sealing around drill pipes with a range of sizes and have advantanges such as low cost and convenience, expatiate on the sealing well mechanism, this paper discusses the structural characterstics of several typres fo variable bore ram, the operation of the varialble bore ram is simulated with the finite element model. the distribution of the stress is analysed, which provides the toudation for optinizing the design of variable bore ram-type blowout preventer
