Abstract: By simulating Q390 steel welding condition, by means of thermal-dilatometer, continuous cooling transformation curve of Q390 steel was measured by Gleeble1500 thermal-simulator, at the same time, the microstructure of different cooling velocity was observed and analyzed by OM and SEM.SH-CCT curve was obtained through continuous cool character analysis and contrast.The results show that phase transformation region contains three parts:the ferrite and pearlite transition zone at high temperature, the bainite transition zone at moderate temperature and the martensite transition zone at low temperature.The microstructure including ferrite, pearlite and granular bainite can be obtained when the cooling velocity is between 0.015 and 0.1℃/s;lots of bainite structure can be obtained at 0.5-1℃/s cooling rate range;the martensite and residual austenite microstructure be obtained when the cooling velocity is beyond 25℃/s.