Abstract: The static continuous cooling transformation (CCT) curves were measured using thermal expansion method, in a Gleeble-3800 thermo-mechanical simulator for 51CrV4 steel.The expansion curves of supercooled austenite during continuous cooling under different cooling rate were determined, simultaneously. With metallographic microhardness method, the effect of different cooling rate on microstructure and performance of 51CrV4 steel was analyzed. The results shows that, with the cooling at 0.5 ℃/s, the phases resulted from the cooling transformation are ferrite and pearlite. With the cooling rate at 1 ℃/s, the bainite is obtained. The cooling rate region for getting martensite is between 2 to 30 ℃/s. When cooling rate is up to 12 ℃/s, the product of the cooling transformation is only martensite.