Abstract: Continuous cooling transformation(CCT) behavior of 0.2Cr and 0.1Cr-0.15Mo fire resistant steel bars under different cooling rates and final cooling temperatures was studied by using thermal simulator Gleeble-3800, and then evolution of structure and properties under room temperature and elevated temperature conditions was investigated.The results show that for 0.2Cr and 0.1Cr-0.15Mo fire resistant steel bars , when the final cooling temperature is 900 ℃, the the cooling rate increases from 2.0 ℃/s to 20.0 ℃/s, the proportion of martensite and bainite increases significantly, and correspondingly the yield strength at room temperature and elevated temperature increase from 390 MPa and 429 MPa to 665 MPa and 1060 MPa, 0.15%Mo can significantly improve the proportion of bainite and its performance at elevated temperature.For 0.1Cr-0.15Mo fire resistant steel bar, when the final cooling temperature increases from 700 ℃to 1100℃and cooling at 1.0 ℃/s, the proportion of ferrite increases firstly and then decreases, the yield strength decreases from 458 MPa to 401 MPa firstly and then increases to 510 MPa.