As the high temperature equipment, the turbine rotor and other components are often subjected to combined high and low cycle fatigue loading in the working environment. When the high and low cycle fatigue interacts, the life of the unit will be reduced greatly. In order to evaluate the life characteristics of rotor steel under high temperature and complex fatigue conditions, low cycle fatigue experiment, high cycle fatigue experiment, and combined high and low cycle fatigue experiment were conducted respectively. Moreover, life characteristics under various experimental conditions were analyzed. Based on the analysis of the relationship between strain and life, it was found that the combined high and low cycle fatigue strain amplitude ratio and life ratio have a power function relationship in double logarithmic coordinates. Therefore, a new model for studying combined high and low cycle fatigue life was proposed.