Due to high steam parameters, high speed, poor working conditions of high and intermediate pressure rotors in 600 MW supercritical steam turbine, it will cause great stress change in the operation process. Rotor burnout occurred due to oil breakoff in a 600 MW supercritical unit, which seriously affected the safe operation of the unit. In order to grasp the stress state of the rotor, and ensure its safety operation, a finite element analysis mode was established by software ANSYS APDL for rotors under cold starting condition. Based on the engineering thermodynamics calculation, the convection coefficients of rotors were calculated, which was used as boundary conditions of the finite element model for the calculation and analysis of temperature field. Then the analytical method of indirect thermo-structure coupling was adopted to calculate and analyze the stress field of rotor, in which the stress distribution and the stress concentration position during the cold starting process of rotor could be obtained. The results show that the equivalent stress of rotor after cutting processing is less than its yield stress, but the stress is larger at the roots groove of governing stage, oil retainer and journal, which can provide technical support for the safety assessment and life management of damaged rotor.