The conventional hardware/software codesign cannot meet the requirement for a PSO algorithm that needs to be changed for different applications. In addition, the architecture of the conventional hardware/software codesign leads to a low processing speed. This paper presents a flexible hardware/software codesign to support various PSO algorithms and increase the processing speed of the conventional hardware/software codesign for various PSO applications. By adopting a simplified hardware architecture, the calculation speed can be improved by reducing the communication overhead. Furthermore, an improved generic particle calculation block (GPCB) is used to enhance the flexibility. It selects an appropriate PSO algorithm without the need for hardware modification to further increase the processing speed. The experimental results proved that the proposed flexible hardware/software codesign can achieve high processing speed and high flexibility with low chip cost.