To improve the lift drag ratio and motion performance of underwater gliders, combining the advanced layout of the joined-wing in aviation and the traditional underwater glider, a joined-wing underwater glider configuration is proposed, which can achieve better lift drag characteristics through optimization. First, numerical simulation of the underwater glider body was carried out, and the validity of the numerical simulation method was verified by comparing the obtained results with the experimental data. Then according to the Computational Fluid Dynamics (CFD) code, the lift drag characteristics of three layouts, the positive staggered, the negative staggered, and the combined empennage were compared and analyzed. The orthogonal layout was chosen as the basic shape of the underwater glider because of its maximum lift drag ratio. Parametric modeling of the shape of the underwater glider was thus carried out. Finally, taking the maximum lift drag ratio as the optimization objective, the Kriging surrogate model was constructed and the EGO algorithm was used to optimize the shape of the joined-wing underwater glider. Results show that the lift drag ratio of the optimized underwater glider increased by 18.42% over that of the vehicle before optimization, and 23.45% over that of the traditional underwater glider. It proved that the new type joined-wing layout has excellent lift drag characteristics in the underwater glider. The research results provide a new way of improving the gliding performance of underwater gliders.