Abstract: To address the technical requirements of deep peak shaving, flexible operation, and safe service of steam turbines, a novel method for online life calculation and closed-loop control of steam turbine components under multidimensional stresses and multiple damage mechanisms was proposed. The online calculation methods for metal temperature, thermal stress, mechanical stress, combined stress, equivalent stress, and limit stress of turbine components were presented. The stress safety factor and the relative stress margin, were proposed and employed for online monitoring of component stresses. Furthermore, transient low-cycle fatigue life loss, accumulated low-cycle fatigue life loss, and remaining calendar life to crack initiation, were introduced for online lifespan monitoring of components. A closed-loop control strategy for turbine speed and load was established based on the online-calculated stress and lifespan values, and was applied to the closed-loop control of rapid speed ramping, fast load variation, and safe operation. Practical application cases of stress and lifespan closed-loop control for ultra-supercritical 1 000 MW-class steam turbines were provided. Results indicate that by online calculation of key stress and lifespan parameters, and through closed-loop control of speed and load ramp rates, long-term operational life and service safety of steam turbines under flexible operation can be effectively ensured.