Abstract: The MIKE21-BW numerical model is used to study the long-period wave generation mechanism of the harbor basin based on the results of the physical model test. By comparing and analyzing the physical model test and the BW numerical model, it is found that they are in good agreement. A long-period wave of 192 s is used as the incident wave, and long-period wave oscillations occur in the harbor area, with maximum wave height up to 3.7 times that of the incident wave. Under the action of bichromatic waves with incident wave frequencies of f₁ and f₂, respectively, wave components with frequencies △f, 2f₁-f₂, 2f₂-f₁, 3f₂-2f₁, f₁+f₂ are generated due to the nonlinear interaction between waves. Long-wave oscillations occur in the harbor basin when low-frequency waves tend to converge to the intrinsic frequency of the basin. The long-period waves are generated under nonlinear interaction between the wave group with a spectral peak period of 10.2 s. The long wave height is positively proportional to the incident wave steepness H₀/L while inversely proportional to the wave direction distribution range, and unidirectional irregular waves produce the most violent long-wave oscillations.