Abstract: To improve the calculation accuracy of online monitoring of steam turbine rotor stress, the simplified calculation methods of the stress field and the temperature field were systematically proposed. Taking the high-pressure rotor of the 300 MW turbo-generator as an example, the temperature field and stress field under cold starting conditions were analyzed by simplified calculation methods and a finite element software. The equivalent stress of the dangerous part was predicted by introducing a correction coefficient. Results show that comparing the results obtained by simplified calculation methods with the results obtained by the finite element software, the maximum deviations of the rotor outer surface and inner temperature appear in the initial stage of cold starting, and the outer surface equivalent stress has a large deviation in the initial stage and later stage of cold starting.The predicted results were in good agreement with the simulation results of finite element software by using the support vector regression（SVR）based on cross-validation, which could meet the accuracy standards of engineering practice.