Flow past a circular cylinder is a classical topic in ocean engineering application, such as the marine riser, oil pipeline, etc. When the ocean current flows around cylinder structures, shedding vortices will appear alternately in the wake of the cylinder at a certain Reynolds number, which is harmful to the service life of ocean engineering structures. Among the abundant active and passive methods of flow control, the splitter plate behind the circular cylinder is a popular choice to improve the flow field of the circular cylinder. It should be noted that the motions of the splitter plate are neglected because most of the present studies treat the splitter plate as rigid body. Therefore, the Fluid-Structure Interaction (FSI) effect between the fluid and the splitter plate is taken into account in the present study. What's more, a new idea with bidirectional splitter plates are proposed to improve the flow field with beneficial effects. Correspondingly, the relationships between the ratios of RMS lift and mean drag coefficients by original circular cylinder with different configurations of the splitter plate are given.