Abstract: In order to study the moisture absorption behavior and performance degradation law of 2D braided composites under long-term moisture-load coupling, a moisture-load coupled aging device was designed. The moisture absorption test and tensile test after moisture absorption of carbon fiber reinforced epoxy resin (T300/H69) plain woven composite material under different stress levels were carried out. The results show that the moisture absorption of T300/H69 braided composites is positively correlated with the tensile prestress, and increases with the increase of tensile prestress. Compared with the effect of water alone, the elastic modulus and strength degradation of the material under moisture-load coupling are more obvious. After 432 h at 140%σ_s (σ_s is yield stress) prestress, the elastic modulus and failure strength of the braided composites decreased by 55.9% and 35.4%, respectively. In addition, the degradation mechanism of braided composites under long-term moisture-load coupling is further revealed by macro and micro section analysis. Based on Shiva's residual strength theory, the residual strength model of composites under moisture-load is improved, and the prediction results are good, which provides guidance for the durability design of composites in complex environment.