The creep strength of weldment for high Cr ferritic steels decreases due to Type IV damages in the heat affected zone during long-term services at high temperatures. It is important to predict initiation and growth of creep voids and cracks in weldment. This paper clarified the Type IV crack initiation and growth properties in fine-grained HAZ of weldments for tungsten strengthened high Cr steels. On the basis of experimental results, the computational simulation for Type IV crack growth behavior was conducted. The effect of multiaxial stress condition on vacancy diffusion and crack initiation was discussed.