Abstract: Gleeble-3500 was used to simulate the thermal cycle processes of bainite steel used for frog. The microstructure and properties of HAZ were investigated by optical microscopy(OM), scanning electron microscopy(SEM), transmission electron microscopy(TEM) and hardness test, respectively. The start temperature of austenite transformation, the end temperature of austenite transformation and the phase transition temperatures under different cooling rates were measured by the tangent method from the expanding curves. According to the experimental results, the simulated heat affected zone continuous cooling transforming(SHCCT) diagram of the bainite steel was constructed.SHCCT diagram provides basic data for the research of its weldability. It could be used to predict microstructure and properties of HAZ and optimize welding and repair welding processes of bainite steel frog.