An optimized wave rotor refrigerator (WRR) that can convert part of the expansion work into shaft work to improve the refrigeration performance is obtained by the optimization method. Bézier curve is used to establish a two-dimensional simplified model, and response surface method and Non-linear Programming by Quadratic Lagrange (NLPQL) optimization algorithm are used to search for the optimal wave rotor structure. The results show that the optimized wave rotor shape is rear-back bending. Compared with the original rotor, the isentropic expansion efficiency of the optimized rotor is higher under different pressure ratios and relative velocity, and changes more gently under different pressure ratios. Moreover, the expansion power of the optimized rotor is mainly converted into shaft power, while the pressure energy and thermal energy increase at the hot end are relatively small. The pressure fluctuations on the inlet and outlet sides of the optimized rotor are smoother, and the compression waves that are constantly reflected during the low-temperature exhaust stage have a smaller intensity, which helps to improve the performance of WRR. The optimized rotor can significantly reduce the entropy production in the refrigeration process, especially the entropy production by velocity gradients. When the pressure ratio is 2.0 and relative velocity is 23 m/s, the isentropic expansion efficiency increases from 56.8% of the original rotor to 62.08% of the optimized rotor.