The work aims to design a bionic propeller of underwater vehicle, in order to better realize the stable navigation of underwater vehicle at low speed in the ocean pasture observation environment. Based on the principle of structure bionics, the bionic design method of dynamic structure was proposed. The design process included selection of bionic objects, extraction of dynamic structural features, matching of biological features and products, innovative design of product integration and design evaluation. With the underwater observation vehicle propeller as an example, the shape and structure of bluespotted ribbontail ray pectoral fin in undulation propulsion were imitated, and the bionic design of dynamic structure was carried out to the shape and function of the bionic propeller step by step. The pressure distribution on the surface of undulating fin was obtained through the hydrodynamic simulation evaluation. The simulation results showed that the undulating fin could generate certain thrust, which verified the feasibility of the bionic design method of dynamic structure. The bionic propeller has the characteristics of stable navigation at low speed, which can effectively improve the observation ability of ocean pasture. The bionic design method of dynamic structure can provide reference for the structure design of bionic propeller.