To study high temperature sealing performance of metal Oring for offshore heavy oil thermal recovery tools, the axisymmetric finite element analysis model of metal O-ring was established to calculate contact pressure and shearing stress in high temperature.The influence factors of metal Oring high temperature seal were studied and the theoretical results were tested by experiments.The results show temperature variation has an obvious impact on the strength and seal performance of meal O-ring.The maximal contact pressure and shearing stress of metal O-ring are increased nonlinearly with working pressure rising, which results in higher seal performance and lower strength of O-ring.The metal O-ring has optimal seal performance in high temperature for 12%-16% initial compression ratio and meets sealing requirement for 350℃ heavy oil thermal recovery tools.The theoretical results have been verified by experiments.