Abstract: Research on the parameters of structural strength is essential for composite structural design. However, the effects of structural size on strength under different hygrothermal environments have been less investigated. Numerical and experimental methods were adopted to study the influence of humidity, temperature and width to diameter ratio(W/D) on T800/X850 carbon fiber reinforced epoxy resin composite (CF/EP) open-hole laminates compression strength. The parameters of the research specimens were designed, and results of the open-hole composite laminates compression failure under different hygrothermal environments were obtained by the tests. A progressive damage model was established to analyse the effects of humidity, temperature and geometric parameters on composite laminates compression strength by using the existing progressive damage methods of composites considering the influence of hygrothermal environments. The good consistency between the numerical and experimental results validates the model. Combined with the experimental and numerical analysis, the influence law of the parameters was revealed. The research shows that hygrothermal environments has a significant effect on compression failure loads of T800/X850 CF/EP open-hole laminates. Compared with the room temperature and dry(RTD) conditions, the room temperature and wet(RTW) conditions and the elevated temperature and wet(ETW) conditions compressive failure loads are reduced by 7.75% and 14.68%, respectively. The failure modes under RTW conditions and RTD conditions are close to each other. The failure modes of ETW conditions are different and the failure area is larger. The compressive failure strength increases with the increase of the W/D in RTW conditions and RTD conditions, and the rates of growth are similar. The rate of growth in ETW conditions increases slower than the former two.