Abstract: Unidirectional carbon fiber reinforced epoxy resin composites (CFRP), glass fiber reinforced epoxy resin composites (GFRP) and flax fiber reinforced epoxy resin composites (FFRP) were manufactured with fiber volume fraction of 60vol% to compare the hygrothermal durability of composites. Water absorption tests were conducted at 23℃, 37.8℃ and 60℃. The swelling rate in the thickness direction, tensile properties and interlaminar shear properties were also monitored, and the time-temperature superposition principle was used to predict the water absorption and mechanical properties. The results show that the water absorption behaviors of three kinds of compo-sites conformed to Fickian's law in the early stage and gradually deviated in the later stage. In terms of water absorption performance, FFRP has the highest diffusion coefficient, saturation water absorption rate and swelling rate. In terms of mechanical properties, the tensile properties of CFRP are almost unchanged with the increase of aging time, while the interlaminar shear strength decreases slightly, and the tensile properties and interlaminar shear properties after drying are the same as those without aging, which indicate that no irreversible changes occurred in CFRP. The tensile strength and interlaminar shear strength of GFRP decrease a lot after aging, while the tensile modulus decrease less. The tensile properties are partially restored after drying, while the interlaminar shear strength is barely restored, which indicate that irreversible changes such as hydrolysis of glass fibers and interfacial debonding occurred during the aging process. Due to the plasticization of flax fibers after aging, the tensile strength of FFRP increase slightly while the tensile modulus and interlaminar shear strength decrease sharply and then remaine stable. After drying, the tensile strength decrease significantly, while the tensile modulus and interlaminar shear strength increase significantly, which are related to the changes of plasticization, expansion and degradation of fiber and matrix. From the long-term performance of the three kinds of composites, it can be seen that the long-term mechanical properties retention rates of CFRP are good, while that of GFRP are poor, and FFRP has an advantage in tensile strength retention rate. The results can provide a theoretical basis for the selection and design of engineering materials under hygrothermal environment.