Abstract: The kenaf fiber(KF) was modified with the alkali peroxide in the aqueous solution. The refined KF-cotton fiber(KF-CF) blended fabrics with different blending mass ratios and KF-CF/epoxy(EP) composites were prepared. The single fiber tester, microscope, FTIR, TG and SEM were used to study the effect of fine treatment on the properties of KF. The best blending mass ratio was obtained by analyzing the mechanical properties of KF-CF/EP composites. The hygroscopicity of KF-CF/EP composites under hydrothermal and chemical conditions was investigated at the optimum blending ratio. The results show that the diameter of KF decreases by 30.66%, the Young’s modulus increases by 31.24%, the softness increases by 13.20%, and the thermal stability improves after refinement treatment. The KF-CF/EP composite with mass ratio of 40∶60 has the best mechanical properties with tensile strength of 101.90 MPa and flexural strength of 189.64 MPa. In the humid and hot environment, the longer the time and the higher the temperature, the higher the water absorption rate of the KF-CF/EP composite, and the alkaline environment leads the water absorption rate of the KF-CF/EP composite to increase.