Abstract: The flow characteristics of a circular cylinder with a splitter plate are investigated experimentally with Particle Image Velocimetry (PIV), and the effects of the splitter plate on the evolution of turbulent structures in the flow around the cylinder are examined. The Reynolds number is Re = 3.9 × 10³, and the ratio of the splitter plate length L to the cylinder diameter D is L/D = 0～2.50. The results show that the length and the area of the recirculation region significantly increase as L/D increases from 0 to 1.00, and the effects of L/D on the characteristics of the recirculation flow behind the cylinder are small for L/D ＞ 1.00. The evolution of turbulent structures is affected by the splitter plate. For L/D ＜ 1.00 the shedding of the wake vortex is suppressed by the splitter plate, and the Strouhal number (Sr) is decreased. As L/D increases from 0 to 1.00, there is a 26.34% decrease of Sr. In addition, the cylinder wake vortex induces the formation of the secondary vortex with opposite direction of rotation in the trailing edge of the splitter plate, and the secondary vortex moves upstream along the plate. For 1.00 ≤ L/D ＜ 2.00, the splitter plate interacts with the cylinder wake vortex, and the wake vortex breaks down into some small-scale wake vortices. For L/D ≥ 2.00, the wake vortex is reattached on the splitter plate, and the secondary vortex is mainly distributed behind the cylinder. As L/D increases, the splitter plate reduces the intensity of turbulence fluctuations behind the cylinder.