This paper aims to establish a control-oriented statespace model for the M4 wave energy converter for the purpose of controller design. The Euler-Lagrangian equation is used to describe the dynamics of M4 in a unified and concise format. The linear wave radiation damping term is expressed as a state-space subsystem, which is then integrated into a state-space model for the whole device. A model order reduction technique is used to reduce the order of the state-space model. The fidelity of the resulting state-space models with different orders is validated in both frequency domain and time domain. The result of this paper paves the way for the future research on developing model-based controller for M4 device to further improve its energy conversion efficiency. The modeling procedure can be transferred to other types of multi-float multi-motion WECs.