Based on performance requirements, the wing of a light fixed-wing UAV(unmanned aerial vehicle)constructed by full carbon fiber reinforced epoxy is designed with features of light weight, high strength,high stiffness and maximum take-off structural mass of 10 kg. The three dimensional structure model of the wing is created based on aero-dynamic performance analysis and geometry design. The "closed rectangular cross-section caps" is adopted in the box-type wing spar, which increases the anti-twisting ability of the wing structure. The finite element model of the wing structure is established. Based on the strength criterion of maximum stress, the strength of the wing structure is checked. The stiffness and stability of the wing structure is also checked. It is show that stress concentration occurs in the wing root area of bolt holes, and the initial strength of the wing is determined by the stress state of this area. Buckling may occur on the spar cap section at the wing root and the skin around under bending load. The laminate structure of the skin is optimized. The weight of the wing skin decreases by 121.6 gram after optimization, about 11.94% of initial structural mass of the wing.