Abstract: Composite laminates are inevitably subjected to different degrees of hygrothermal environments in practical applications, and the hygrothermal environments will have a significant impact on the mechanical properties of the laminates, so it is necessary to investigate the influence of hygrothermal environments on the mechanical properties of the delamination. In this study, specimens were designed for four treatments: room temperature/dry, room temperature/wet, 70°C/dry and 70°C/wet, and mode I and mode II static delamination tests were carried out. The effect of hygrothermal environments on the delamination properties of laminates was analyzed, and it was found that high temperature would increase the mode I fracture toughness while has less effect on the mode II fracture toughness; humidity would reduce both mode I and mode II fracture toughness; and the mode I fracture toughness would increase under hygrothermal environments while the mode II fracture toughness would not change much. Numerical simulations of DCB and ENF tests were established based on the cohesive zone model (CZM), and the effect of the hygrothermal environments on the engineering constants of the composite material was taken into account. The validity of the numerical model was verified by comparing the simulated results with experimental results under different hygrothermal environments.