Based on the dynamic mesh technology, this paper uses the commercial software STAR-CCM + to simulate the propulsion performance of a bionic undulating fin under the influence of the sidewall surface. Through the thrust coefficient and lift coefficient, the propulsion performance of undulating fins with different wave frequencies and wavelengths at different side wall distances is analyzed. It is found that the influence of the side wall on the propulsion performance of a bionic undulating fin may be positive or negative. At the same time, the vorticity field structure under different motion parameters and wall distances are analyzed, and the mechanism of the influence of the side wall on the propulsion performance of undulating fin is explained from the perspective of vorticity field, which provides a theoretical basis for the design of bionic undulating fin underwater vehicle that can operate efficiently in special environment.