In order to improve the maneuverability and endurance of bionic system in the water, a three-joint bionic goldfish system was designed based on the body and/or caudal fin (BCF) swimming mechanism. The research focuses on the modular system design, multi-modal motion, fixed-depth and fixed-course motion, and underwater endurance of bionic goldfish. Through the design of PID controller, the bionic goldfish can achieve high precision control and stable fixed depth and navigation movement. The feasibility of the bionic goldfish system designed in this paper is verified in the actual water environment. The test results show that the bionic goldfish system has good maneuverability and stability.