Abstract: The finite-element model of extended mild-slope equation is used to simulate the oscillation between a semi-circular bay and a slender harbor with variable water depth. A numerical model test shows that incident waves and the radiation damping of the narrow-long harbor are changed due to the bay which influences the resonant features of the harbor. Correlation analysis shows that the bay plays a leading role in the coupled resonance if the ratio of water volume between the bay and the harbor is much higher than 2.5, resulting in a positive correlation between the amplification diagrams of junction and harbor in intensity and trend. Conversely, bay and harbor hold equal status in a coupled oscillation, leading to a positive correlation only in intensity.