Abstract: In this study,finite element analyses were performed to simulate hydrogen diffusion behavior in heterogeneous welded joints.The results indicated that:(1)for 20MnNiMo welded joint,the hydrogen concentration within weld metal decreases in a monotonic manner as time elapses,in contrast,hydrogen concentration outside the fusion zone goes through a local maximum.Because of different diffusivity and solubility in different region of welded joint,the hydrogen concentration within heat affected zone(HAZ) will exceed that within weld metal and base metal some time later;(2)preheating decreases hydrogen concentration within weld metal rapidly and shortens the time to reach a peak hydrogen concentration within HAZ;(3)postheating may accelerate hydrogen removal from welded joint and reduse the peak hydrogen concentration within HAZ and shorter time of reaching the pear value.