Abstract: The gas-cooled reactor steam superheater tube plate made of 800H austenitic alloy was taken as the research object. By the simplified elastic stress analysis method of volume 2/3 of the R5 procedure, combining with finite element simulation, the steady-state cyclic stress and strain of the tube plate experienced combined impact of hot and cold fluids were estimated. Creep-fatigue damage analysis was carried out, and the influence of cyclic loads on the failure behavior of key positions of the tube plate was studied. The creep-fatigue life was predicted. The results show that after one single cycle consisting of steady-state load retention→cold fluid impact→steady-state load retention→hot fluid impact processes, the critical point of the tube sheet appeared at the junction between the tube sheet and the tube box shell. Creep damage was the dominant factor leading to the failure of the tube sheet, and its cumulative rate was much higher than that of fatigue damage. The fluid impact significantly affected the stress-strain response at key positions through the intense fluctuation of thermal stress, thereby determining the evolution path and cumulative efficiency of creep-fatigue damage, and affecting the service life of the tube plate structure. Under the small temperature fluctuation condition, the cold fluid impact directly aggravated fatigue damage while simultaneously intensifying creep damage, strengthening the interaction between creep and fatigue, and accelerating structural failure. The hot fluid impact could reduce the plastic deformation and inhibited the cumulative of creep damage, having a relative small effect on the structure service life. Cold fluid impact was danger than hot fluid impact. In the small temperature variation environment that required temperature adjustment, the hot fluid impact condition should be given priority.