Abstract: Behavior for of moisture sorption of aromatic polyamide fibers(AF) was studied, the diffusion coefficient was calculated and, in the meantime, the effect of moisture sorption of composite on ILSS was studied. It is found that the moisture sorption of AF was increased after plasma treatment, and the ILSS of composite was not lowered but raised. After the fibers were soaked in water, the drop percent in ILSS of composite was decreased; especially for moisture, the drop percent in ILSS of composite was evidently decreased. This is because the chemical bond of interface was introduced after plasma treatment, and its interfac, cohesive strength and water-resisting property were increased.