Abstract: In order to improve the uniformity of microstructure and comprehensive mechanical properties of 45 steel after rolling, the controlled rolling and controlled cooling process simulation test was carried out by thermal simulation testing machine. Through single pass simulated rolling test, the dynamic recrystallization behavior of 45 steel during rolling process was studied, the critical point and phase transition point were determined, the dynamic recrystallization diagram of the test steel and the continuous cooling transformation curve of the supercooled austenite were drawn, and the controlled rolling and controlled cooling process window design of 45 steel was completed, which provided a reliable theoretical basis for the formulation of controlled rolling and controlled cooling process of 45 steel.