Abstract: Three thermal conduction models,i.e.the transient planar heat source model,the initial temperature of molten pool model and the moving heat source model,are presented to describe the temperature development in the vicinity of a long welding line in a large flat-plate.Analytical solutions are given for these models.Based on these solutions,the relation between the temperature and the width of the heat affected zone is derived with explicit functions.Furthermore,the criterion was proposed to indentify for the impact of the heat dissipation from the plate surface on the conduction process.