Abstract: Both the moisture absorption behaviors of fiber reinforced resin composites in hot and humid conditions and their influencing factors are introduced. The effects of hygrothermal aging on heat-resistant property and mechanical property of fiber reinforced resin composites are summarized, and the hygrothermal aging mechanism is also analyzed. The moisture absorption behaviors of most fiber reinforced resin composites agree with Fick′s law of diffusion during the early stage of the hydrothermal exposure process. Moisture absorption can cause the performance degradation of composites due to plasticization, hydrolyzation, cracking of matrix and damage of fiber/matrix interface. In addition, some suggestions on hygrothermal aging research of fiber reinforced resin composites are proposed.