Abstract: The distribution of the electromagnetic force around a cylinder covered by electromagnetic actuators is obtained firstly by solving Maxwell equation system, and then such a Lorentz force is added to the momentum equation of flow governing equation system. The numerical simulation is carried out to simulate and analyze the flow structures around a circular cylinder and its lift/drag characteristics in a weakly conductive fluid under various combinations for electromagnetic interaction parameters and electromagnetic actuator widths when the Reynolds number Re=200. The results show that for the case of small electromagnetic actuator width, the separation point of the flow around a cricular cylinder is easier close to the back stagnation point, and the electromagnetic force has small influence on the total drag, but it has obvious influence on the pressure and friction. For the case of large electromagnetic actuator width, the cylinder wake is easier to become jet flow, and the total drag decreases as the electromagnetic interaction parameter and the electromagnetic actuator width increase. Moreover, for the case where the electromagnetic force is insufficient to completely inhibit periodic vortex shedding, the lift amplitude decreases as the electromagnetic interaction parameter increases, but it first has an obvious reduction and then a slight increase as the electromagnetic actuator width increases, and the lift pulsation frequency increases as electromagnetic interaction parameter and the electromagnetic actuator width increase. The results imply that the electromagnetic force can effectively improve the flow structure around a cricular cylinder to achieve the purpose of reducing the drag and inhibiting the lift fluctuation, therefore the flow structures can be improved effectively by the electromagnetic force.