In order to reveal the influence of hygrothermal environment on the mechanical properties of aeronautical composite connection structure, a numerical simulation model of composite interference-fit structure was established based on the mechanical ontological relationship and continuous damage model of composites under the hygrothermal environment with the object of composite interference-fit structure. The model was utilized to analyze the static strength and damage failure of interference-fit structures in the hygrothermal cycle of 0 days, 30 days, 60 days, 90 days and 120 days respectively, and was validated with the hygrothermal aging experiment. The results show that the ultimate load of the composite interference-fit structure decreases by 3.33%, 5.63%, 8.83% and 10.81% respectively, as the hygrothermal cycling period increases from 0 days to 120 days; the hygrothermal environment causes the aging reaction within the composite matrix, results in a rapid deterioration of the matrix performance, while has little effect on the fiber damage. The validity of the numerical simulation model was verified by comparing the experimental results with the simulation results.