Abstract: The material strength reduction of oil and gas well casing inevitably occur in the service process, and the residual strength affected by service has a significant impact on wellbore safety. The P110H casing material for thermal recovery well was selected, which was subjected to high temperature aging and low cycle fatigue service damage loading, and then tensile test was conducted to obtain the residual strength of the material after damage. The results show that both high temperature aging and low cycle fatigue service lead to the decrease of residual strength, and the decline law presents exponential function characteristics. The ultimate strength loss is about 10% after high temperature aging, and the residual strength affected by low cycle fatigue still decreases in the stable stage. The damage mechanism shows that the strengthening ability of the high temperature aging material decreases during deformation, and low cycle fatigue makes the distribution of dislocations in the grains uneven, which leads to the instability of the grains. The mechanism of the two damage modes is independent of each other. The residual strength after linear superposition of high temperature aging damage and low cycle fatigue damage can be used as engineering prediction model of strength.