Abstract: The continuous cooling process of ultra-low carbon SiCrMn2Ni4 steel was simulated. Microstructure was observed and analyzed by metallographic microscope, SEM and TEM. The results showed that only granular bainite and lath bainite existed in the experimental steel after continuous cooling. With the increasing of cooling rate, granular bainite turned into lath bainite gradually. When the cooling rate increased to 5 ℃/s, a mixture of granular bainite and lath bainite appeared. When the cooling rate was no lower than 20 ℃/s, the microstructure was all lath bainite.