Abstract: For the assembly gap in composite airframe structure, an optimization method based on genetic algorithm was proposed to optimize the size and layout of pressing force, in which damage caused by pressing force was considered. Combining with finite element analysis, considering the interference between pressing points, with laminates delamination as the constraint condition and elimination rate of gap as the objective function, the optimization model with size and layout of pressing force was established. Taking composite win box as an example, establishing finite element model based on cohesive element, the optimization method was applied to optimize pressing force on composite panel. Then, with the optimum size and layout of pressing force, the elimination rate of gap, delamination damage, stress and strain were calculated and analyzed. The results demonstrate that:the optimum pressing force makes stress and strain distribution more uniform; elimination rate of gap is improved dramatically compared with the traditional one without laminates delamination. When the initial assembly gap is 0.2-0.8 mm, the elimination rate of gap is increased to 77.4%-100%, which is 19.2%-177.8% higher than that before the optimization.