X80 pipeline steel was heated to above the austenitizing temperature (920℃), held for 7 min, and cooled in different cooling media (10wt% NaCl solution, tap water, engine oil, air, cooling rate decreased in turn). The microstructure and mechanical properties were studied. The results show that with decreasing cooling rate, the strength and hardness of the test steel decreased, the plasticity increased, and the impact energy increased first and then decreased. After cooling at relatively high rates (in NaCl solution and tap water), bainite ferrite and a few martensite laths were formed in the microstructure, and many dislocation structures and a few carbides were found in martensite laths; the test steel had high strength and low deformability. After cooling at a relatively low rate (in air), polygonal ferrite, bainite ferrite and a few block martensite-austenite structures were formed in the microstructure; the strength and impact toughness of the test steel were low. After cooling at a moderate rate (in engine oil), a duplex structure of bainite and ferrite was formed in the microstructure; the multitude direction distributed bainite and high density dislocation ferrite adjacent to bainite led to good comprehensive mechanical properties and high resistance to large deformation of the test steel.