Abstract: A novel three dimensional temperature analytical model for gas metal arc welding(GMAW)was presented, in which the effect of droplet entropy on welding penetration during welding was considered.The energy of heat input was considered mainly as two parts including electric arc heat and droplet entropy.Electric arc heat was assumed to take a semi-ellipsoidal distribution and droplet entropy was looked as two Gaussian distributed point heat sources. The finite element analytical solution was obtained by solving novel heat source heat conduction equation.Bead-on-plate welding were performed on a carbon steel.To investigale the validyty of the model, the actual isotherms of the specimens cross sections at various time from the arc start point were compared with those of the simulation result.The result shows the novel model is valid.