Abstract: The critical points of hot rolled Q345 steel were determined and analyzed by calculation method, expansion method and differential scanning calorimetry (DSC) method, respectively. The accuracy, consistency and applicability of the three measuring methods were discussed systematically. The results show that the critical points determined by calculation method, expansion method and DSC method were consistent. The critical points of A_c1 and A_c3 of hot rolled Q345 steel were about 730 and 860℃, respectively. For the determination of the critical points of hot rolled Q345 steel, the expansion method is recommended to be based on YB/T 5127-1993, and the DSC method is recommended to be used at the heating rate of 10-20℃ ·min^-1.