Abstract: The surfaces of glass-fiber reinforced cyanate-ester composite,an advanced material in aerospace/energy/transportation industries,were activated by plasma irradiation.The influence of the separation between plasma-source and sample on the surface properties was investigated.The preliminary results show that the distance had a major impact.To be specific,as the distance increased,the surface activation changed in an increase-decrease manner.At the optimized distance(150 mm) and voltage(1000 V),plasma irradiation significantly improved the wettability and increased the surface energy/roughness/density of chemical-radicals,including the nitro/ketone/carboxyl/alcoholic/hydroxyl groups,because of the plasma-induced fragmentation of cyanate ester resin.A smaller distance and a higher voltage strongly etched glass-fiber,and a larger distance and a lower voltage considerably weakened the surface activation because of much reduced plasma energy.Possible mechanisms were tentatively discussed in a thought provoking way.