Influence of splitter plate length on characteristics of flow past a circular cylinder at high Reynolds numbers is investigated using large eddy simulation (LES). Lift coefficients, drag coefficients, Strouhal numbers and vortex shedding patterns of different splitter plate lengths are compared and analyzed. The results of analysis show: based on the time histories of lift coefficients and drag coefficients, the splitter plate lengths could be divided into three regimes, which are the stable regime I (when the splitter plate length L=0D, D is the diameter of the circular cylinder), the unstable regime II (L=0.5D-1.0D), and the stable again regime III (L=1.5D-8.0D). When splitter plate length changes from regime I to regime II, there is a sudden drop of Strouhal number. When splitter plate length changes from regime II to regime III, there is a sudden increase of Strouhal number. With the increase of splitter plate length, the vortex shedding pattern of flow field changes from 2S to 2P.