<p>The wave attenuation performance of a floating breakwater is important in engineering applications. On the basis of potential flow theory, the analytical and simplified solutions of the transmission coefficient of a floating breakwater are deduced via velocity potential decompositions and eigenfunction expansions. The effects of the floating breakwater configuration, working sea state and motion response on the wave attenuation performance are described, facilitating a deeper investigation into the wave attenuation mechanism of the breakwater. The results indicate that the width and draft of the breakwater, incident wavelength, and motion response significantly affect the transmission coefficient of the breakwater. The wave passability rate, <i>α</i>₁ (<i>α</i>₁ = 0.5−2<i>B/L</i>), is defined to qualitatively explain why long-period waves are difficult to control and attenuate. The radiation effect caused by the motion of the floating breakwater on the transmission coefficient is relatively complex, and the wave attenuation efficiency of the breakwater can be improved by optimizing the motion response. The incident wavelength and breakwater width are selected as the control parameters, and transmission coefficient charts of the floating breakwater for two-dimensional conditions are drawn, providing technical guidance for the configuration selection and design of the floating breakwater.</p>