Abstract: In this paper,correction factors for heat input to different welded joints have been derived,beed on the theory of heat flow distribution.Three types of modification factor are discussed.These correspond to thick,thin,and finite plate thickness conditions.Emphasis has been laid on the discussion of the modification factors for thick plate.The modified temperature are substituted into the original analytical expressions in order to check the theory.The calculated results show a satisfactory correlation with FEM and experimentally obtained dada.