All along, human exploration of the ocean has never stopped, and bionic fish robots have been produced. Currently, bionic fish have been used in a range of fields, including underwater archaeology, water quality monitoring, and other fields, because of their camouflage and flexibility. The bionic fish also can perform observation, reconnaissance, and other jobs, reduce battle risks, and play a crucial role in contemporary military tasks. It is increasingly being implemented in the military sphere. The efficacy of the bionic fish’s tail mechanism in terms of swimming and reconnaissance is crucial to the design of the fish. However, multiple servo joints are frequently used in the current bionic fishtail system, which increases the likelihood of failure. This research suggests a fishtail design strategy based on the transmission mechanism to operate more steadily. After analyzing the existing bionic fish mechanical structures, research proposes the schemes of living in three mechanical structures. By combining the actual fish body size, the comprehensive modeling design was carried out using Solid Work software, and the motion performance analysis of the mechanism was analyzed by Adams software. The experimental results provide a theoretical and reference for the actual design of bionic robotic fish.