Critical investigation of the transient temperature distribution is important for maintaining the quality of the Submerged Arc Welding of structural steel plates. The aim of this paper is to derive an analytical solution to predict the transient temperature distribution on the plate during the process of Submerged Arc Welding. An analytical solution is obtained from the 3D heat conduction equation. The main energy input that is applied on the plate is taken as the heat lost from the electric arc. The kinetic energy of filler droplets, electromagnetic force and drag force are also considered as input to the process. The electric arc is assumed to be a moving double Central Conicoidal heat source which follows approximately the Gaussian distribution. It is observed that the predicted values are in good agreement with the experimental results. The heat-affected zone (HAZ) width calculation is also done with the help of the analytical solution of the transient 3D heat conduction equation. Analysis of microstructural changes is critically investigated to comprehend the HAZ softening phenomenon and for the validation of the predicted HAZ width.