Abstract: The welded joints of P91/10CrMo910 dissimilar steel using two types filler materials 2.25Cr-1Mo and 5Cr-0.5Mo were made according to the real condition and their properties were investigated by measuring the impact toughness, microhardness distribution and observing the microstructure. The effects of the second tempering on the joint properties were discussed. The results showed that the toughness of the joint using 2.25Cr-1Mo was higher and that of the one using 5Cr-0.5Mo was lower; By double tempering the microstructures of the joints were improved and the toughness of the joints increased in some way; There were obvious difference of microhardness on both sides of the fusion line and there was an unmixed zone in the weld adjacent to P91 due to the microstructure changing and carbon diffusion across the fusion line. Microhardness of the joints after double tempering was lower than that of the joints without heating treatment and their microhardness distributing curve were similar.