Abstract: The temperature field distribution of heat-affected zone(HAZ) in weld joints of bainite steel and U71Mn steel and the technical parameters of upset pressure of flash butt welding were determined by using the Gleeble thermal simulation test technology.After some small specimens of bainitic crossing steel and U71Mn rail steel were welded with a miniature flash butt welder by using the results of the parameters to determine the technical parameters of flash butt welding experiment, bainitic steel crossing and U71Mn steel rail were practically welded with Gaas-100 direct current flash butt welder.The mechanical properties, including tensile toughness, impact test and hardness, and the microstructure of welded joints were analyzed.The results show that the best upset pressure of flash butt welding is about 30 MPa, which the HAZ is very small, and the mechanical properties of the welded joint comes up to the standard of the Ministry of Railway.The welding bainitic crossing steel and U71Mn rail steel by flash butt welding is completely feasible.