Abstract: To address the issues of thermo-mechanical fatigue damage and life management for thick-walled components of utility boilers under flexible operating conditions, a fatigue life calculation method based on nonlinear damage accumulation was proposed, and corresponding anti-fatigue design and its inverse application methods were presented. Fatigue strength verification was conducted for the boiler header tee structure, and the design and optimization of hot start-up scheme for a 700 ℃ class utility boiler were carried out. Results show that the established damage evolution model in the form of a hyperbolic sine function can effectively describe the low-cycle fatigue damage evolution behavior of Inconel 617 alloy under different strain amplitudes. Under the "two-shift" operating mode, the maximum elastic-plastic equivalent strain amplitude of the header tee structure during the hot start-up should not exceed 0.17% to meet 30 a service life requirement. When the hot start-up time of the boiler is reduced to 45 min, the service lives of the header tee structure calculated by Neuber's method and the G-M method, are 38 and 50 a, respectively.