Abstract: In the process of heating and cooling during welding, complete rigidity restraint is not in existence between narrow lath of weldment and the face can not keep to be flat which generate convex and concave.While similar welding residual stress distribution can also be obtained without such plain section hypothesis.No residual compressive plastic deformation exists in the weld metal and there is only tension strain.The traditional view that the distribution of residual compressive plastic strain across the weld metal and near its vicinity is not valid.A new schematic sketch of tensile plastic strain distribution is addressed in terms of near temperature distribution at approximate widest location of the molten pool.The size of tensile plastic strain in the weld metal is A α_l ( T_m - T_r)-( R_rt - R_rc)/E.