Abstract: Taking low alloy steel Q345 welding plate as the research object, stress distribution characteristics in depth direction of weldment before and after PWHT was researched by deep-hole drilling method and indentation strain-gage method was adopted to surface stress. The research results showed that residual stress of weld in original state after welding was distributed in M shape along the thickness direction, and peak value of stress was close to 90% yield strength of weld metal. Stress level of weld after PWHT was relatively low, basically maintaining at 50～70 MPa. By comparing and analyzing characteristics of residual stress in weld before and after PWHT, it showed that deep-hole drilling method could well characterize three-dimensional residual stress in weld before and after PWHT.Highlights: The deep hole method was used to test the three-dimensional residual stress of the weld before and after heat treatment, and the feasibility of the method in analyzing the residual stress in the weld with large thickness was verified.