Abstract: For T91/TP347H dissimilar steel joints of a supercritical boiler operating for 75, 000 h, the metallographic microscope, the universal material testing machine and the scanning electron microscope were used to study the performance of the joint after long-term service.The results show that the weak area of the dissimilar steel joint is at the T91 fusion line, the formation of chain holes and decarburization layer in the region greatly weaken the mechanical properties, and the formation of oxidation gap accelerates the cracking of the joint. The impact performance of each area of the dissimilar steel joint is significantly reduced, and the impact performance of the weld metal is the lowest, which is only 66 J.