The E690 grade offshore platform steel was obtained by top and bottom blowing converter,curved spray continuous casting machine and thermo-mechanical control processing(TMCP).The static continuous cooling transformation curves(CCT curves)of the rolled plate were drawn by adopting thermal expansion method and metallographic analysis.The microstructures at different cooling rates were observed by optical microscope(OM)and scanning electron microscope(SEM).Results showed that the super-cooled austenite in tested steel was relatively stable and there was little high temperature microstructure transformation at the cooling rate of 0.1℃/s.The regression model of phase transformation temperature and cooling rates were obtained.According to the results of orthogonal experiment,the most optimal heat treatment process was firstly heated at 890℃,wind cooling and then tempered at 630℃ for 60 min.