Abstract: A new wake-oscillator model is presented to predict the response of vortex-induced vibration of a solid cylinder of two degrees of freedom. The strength of a near-wake discrete point vortex is put forward to represent the state variable of the wake oscillator. Based on potential flow theory, the relationship between in-line (IL) or cross-flow (CF) fluid forces on a structure and the vortex strength is quantified, which leads to establish a coupled fluid-structure equation. The model is solved by the numerical method and then the IL or CF amplitude and frequency are obtained. A comparison to the existing experimental results shows that the features of the synchronization domain, lock-in frequency and figure-of-eight trajectory are consistent with the experimental measurements.