The hydrodynamic characteristics of a circular cylinder in two-dimensional unsteady uniform cross flow was simulated numerically by the laminar model with the reasonable mesh used the method of fluent. The focus of this numerical simulation was to research the characteristics of pressure distribution, drag coefficient and lift coefficient, and the Strouhal number was calculated at Reynolds-numbers value of 200. The results agree well with experimental data and other numerical results according to the reference. In order to study the control measures of the flow over a circular cylinder, the different baffles inserted at various locations downstream of the cylinder have been compared. The results shows that the vortex shedding of flow over a circular cylinder could be well controlled by place the baffle at a right position of the downstream medial axis of the cylinder, which could reduce drag and resist vibration.