Long-period wave oscillation leads to extremely terrible wave conditions in the harbor，which seriously jeopardizes the normal docking and operation of ships in the port.The oscillations and amplifications of long-period waves in a harbor are studied by physical model tests.The results show that long-period oscillations obviously occur in the harbor basin under short waves，and the long-period wave height reaches to 0.4 m under 5.47 m incident wave height.Wave energy in the port is amplified in the port at the wave period nearly equivalent to 633，320 and 200 s. Through the comparison of wave energy inside and outside the harbor,it is found that the wave energy outside the harbor at a frequency below 0.008 Hz is far less than the wave inside the harbor, and the long-wave energy inside the harbor area near 320 s and 200 s is amplified by 5 times.The results can be beneficial for the prevention of long-period waves in similar projects.