This paper addresses a platform-based design method of a real-time embedded system for controlling three-dimensional (3-D) swimming of link-based robotic fish. It involves mechanical design, hardware implementation, software design, and central pattern generators (CPG) inspired 3-D swimming control. With the ARM-based microprocessor AT91RM9200, the established hardware is well suited for complex computation environments. Moreover, concerning software design within the framework of the real-time operating system muC/OS-II, each function of the controller represented by a task can be easily added to the embedded system. Both the core hardware and software are realized by a standardized method, which makes the platform easily expandable and manageable. Without significant modification, the developed 3D locomotion controller for robotic fish based on the platform concept can further extend to other control systems.