Abstract: The FEM model of dissimilar welded joints between martensitic heat-resistant steel (T91) and austenitic (HR3C) was established to study the creep failure.The maximum principal stress,von Mises equivalent stress,stress triaxiality were simulated at 600℃ and under the inner pressure of 42.26 MPa.The results show that the peaks of the maximum principal stresses are in the interface of weld/T91 and HR3C/weld on inner surface,and in the vicinity of weld/T91 interface in the distance of 2.96 mm from outer surface.The highest von Mises equivalent stress is in the weld/T91 interface of inner surface, successively,in the weld/T91 interface of 1.29 mm from inner surface,outer surface and 2.96 mm from outer surface.The stress triaxiality in the weld/T91 interface of inner surface is quite high,creep cavities are easily to link interfacial creep cracks.And that,the stress triaxiality in the fine grain HAZ of 1.29 mm from inner surface and 2.96 mm from outer surface are also quite high,accordingly,creep cavities are easily to form type IV creep cracks.Therefore,using stress triaxiality to describe creep cavity expansion and crack development of weld/T91 interface and fine grain HAZ is more reasonable for the dissimilar welded joint of T91/HR3C,and the numerical simulating results are good in agreement with those experiments.