Abstract: The dilatometric curves and continuous cooling transformation (CCT) curves of BM510L steel at different cooling rates were measured in Gleeble-3500 thermal simulating test machine by dilatometric measurement. The microstructure and microhardness of BM510L steel after transformation of austenite in continuous cooling process were studied by optical microscopy (OM) and microhardness tester. The results show that as the cooling rate increases, both the initiate temperature of ferrite transformation and the terminal temperature of pearlite transformation decrease. The bainite is obtained in the microstructure at the cooling rate above 1 ℃·s-1, and the microstructure is totally bainite at the cooling rate of 15 ℃·s-1. The hardness increases with the increase of cooling rate.