In order to investigate the characteristics of flow fields around circular cylinders, a numerical model was developed by combing large eddy simulation(LES)with the characteristic-based operator-splitting finite element method. The model was used to simulate flow fields around a circular cylinder and two circular cylinders in tandem arrangement, and the obtained results agree with the existing results. The simulation results show that, for the flow around a circular cylinder, with the increase of the Reynolds number, the vortexes occurring at the top and bottom surfaces alternatively in the near-wake region gradually approach each other and pass along the horizontal line through the geometric center of the cylinder, and the location of vortex shedding gradually approach the cylinder; for the two circular cylinders in tandem arrangement, with Re=1000, the critical space between the two circular cylinders is 2.25 to 2.50 times their diameters; when the space between the two circular cylinders is smaller than the critical space, vortex shedding does not occur at the rear of the upstream cylinder, and the pressure in the space between the two circular cylinders is stable; when the space between the two circular cylinders is larger than the critical space, vortex shedding occurs, and strong negative pressure regions occur at the top and bottom surfaces alternatively in the near-wake region of the upstream cylinder.