Abstract: The 85 mm Q345 high strength heavy steel plates were prepared through thermo-mechanical controll cooling (TMCP) process.By means of tensile and impact tests,microstructure and fracture morphology observation,the microstructure and properties of the heavy plates were studied.The results indicat that the microstructure of the Q345 steel heavy plates consisted of polygon ferrite and large quantity of bainite at the surface,besides ferrite and pearlite in other positions.The yield strength was up to 320 MPa,elongation was more than 29% and impact ductility was good.The cost of production was reduced without adding microalloying elements and heat treatment process after rolling.The strength and toughness of the heavy plate matched perfectly.