The temperature distribution and cooling rate play an important role in the investigation of heat affected zone of weldment. All the problems such as metallurgical changes, welding thermal stress, welding residual stress and welding deformation in the heat affected zone of welded joint are due to the temperature distribution and cooling rate. In this paper, one dimensional temperature distribution and cooling rate due to transient arc welding heat in the heat affected zone of the base metal are studied. Heat transfer equation for one dimensional heat flow is formed, and solution is obtained. Weld heat input formula is also formed and used. Computed numerical results show a good agreement with the experimented temper color.