Blended-Wing-Body (BWB) civil aircraft possesses so light structure, high lift-drag ratio and low fuel burn that it has been an important topic of future civil aircraft. But internal pressure causes large bending stress instead of skin-membrane stress in BWB non-cylindrical fuselage. For 150 seats BWB fuselage, a composite 3-bay fuselage model is analyzed and two improved configurations of braced fuselage derivatives are designed in this paper. By optimization analysis, the optimized non-cylindrical fuselage structures are obtained in low bending stress and deformation condition, and optimized layer thicknesses ratio of composite material are presented. The optimization conclusions are very valuable and applicable for the fuselage structural design of BWB civil aircraft.