Air plasma processing is introduced as a surface modification technique for carbon fibers to enhance the hygrothermal resistance of carbon fabric/epoxy composites. On carbon fiber surface subjected to 4-min plasma processing, there are 37.6% of carbon species present as -C-O-C groups and 9.3% of carbon species as -COOH groups. The moisture adsorption behavior of composites can be described by Fick's law. Increase in temperature accelerates the initial moisture adsorption rate and results in a higher diffusion coefficient. The decreasing interlaminar shear strength (ILSS) of composites is mainly ascribed to the loss of adhesion at the fiber/matrix interface. A lower equilibrium moisture content of composites is caused by air plasma processing, which leads to the improved interfacial bonding strength and the higher retention rate of ILSS of carbon fabric/epoxy composites. The interface sensitivity and temperature dependence of moisture adsorption for carbon fabric/epoxy composites are discussed. The results presented herein demonstrate an effective strategy for enhancing hygrothermal resistance of carbon fiber-reinforced composites.