Abstract: Metal dusting is a phenomenon of high temperature corrosion, which occurs in carburizing environment. The first step of this corrosion is the diffusion of carbon towards metal matrix. A coupling calculating method on carbon diffusion has been developed based on the finite element program. By this method, the effect of welding residual stress on the carbon diffusion was numerically simulated for the as-welded condition and operation condition of the tube in heating furnace. The diffusion without the effect of stress was also taken into account and compared with those under residual stress. The results show that the highest welding residual stress gradient is near the heat-affected zone(HAZ), and the peak value of carbon concentration exists near this zone. Also the low carbon concentration valley exists at the both sides of the peak value, which is caused by the diffusion of carbon to the high stress zone. In operation conditions, stress relaxation will happen and the effect of residual stress is decreased, which can delay the metal dusting corrosion of the tube. But the influence of the residual stress still exists, the zone near the weld of the tube should be inspected carefully during the inspection period.