Two-buoy wave energy device is a form of oscillating float technology, and it is of great significance to study the power conversion characteristics for development of wave energy devices. This paper established the device's dual-degree of freedom forced vibration equations based on linear wave theory and viscous damping theory, and expression of optimal absorbed power of the device was deduced under condition of the optimum damping. Added masses coefficients, damping coefficients and wave excitation force were calculated by using HydroStar software, then, absorbed power and capture width ratio were obtained. The paper also analyzed effects on power absorption characteristics with the change of geometry parameters of two-buoy wave energy device in actual sea conditions.