In this study, the vortex-induced vibration (VIV) of a circular cylinder at the low Reynolds number of 200 is simulated by a transient coupled fluid-structure interaction numerical model using the combination of FLUENT and ANSYS platforms. Considering VIV with low reduced damping parameters, the trend of the lift coefficient, the drag coefficient and the displacement of the cylinder are analyzed under different oscillating frequencies of the cylinder. The frequency ratio α is a very important parameter, which has been intensively investigated here. The typical nonlinear phenomena of lockedin, beat and phases switch can be captured successfully. The evolution of vortex shedding from the cylinder and the trajectory of the 2 DOF case with varied frequency ratio is also discussed.