Fatigue-creep damage has been recognized as the elemental cause of failure of industrial steel structures exposed to high temperature. In order to better understand the degradation process, a previously developed multi-scale fatigue-creep damage is applied to evaluate the structural damage due to fatigue and creep process. In the model, the relationship between collective behavior of micro-cracks and fatigue damage variable was established and the nonlinear coupling of fatigue damage and creep damage was taken into consideration. Fatigue-creep damage analysis on a series of existing key connection shafts in industrial steel structures at high temperature are performed under different working condition and their lifetime are predicted based on the numerical calculation on the accumulated fatigue-creep damage up to structural failure. The numerical results indicate that the early stage of degeneration process is dominated by creep damage and the fatigue damage rate increases quickly at the later stage. The fatigue-creep lifetime of industrial steel structures varies significantly with different applied stress level and working temperature.