Abstract: The U71Mn G hot rolled rail from Wuhan Iron and Steel(Group) Company was welded by flash butt welding using weld machine of model# YHG-1200^TH. By analyzing the variation of welding current, voltages, displacement, pressure etc., in the welding process with respect to those factors including pre-flash, pulse flash, accelerating flash and upset forging, and combined with the hammer impact test, the study aimed to optimize the welding process parameters. Then analysis on the relations between welding heat input, upset forging and impact numbers was performed. The joint fractured surface and the microstructure were also observed. The study specifically approved that when welding heat input located between 11.5 to 12.5 MJ and upset forging length was inside 15~16 mm, the welded joint can perform well in the hammer impact tests,with good quality and consistency. The fractured surface of the joint welded in optimized parameters had no obvious defects. The microstructure of the weld the heat affected zone are pearlite with a small proportion of ferrite, No martensite, bainite or other defects was found in the weld structure.