MIKE21 BW numerical model was verified by the wave filed simulation of port TEMA,which matched well with physical model test results.The wave conditions in the harbor under unidirectional and multi-directional irregular waves were studied and their variation laws caused by different wave directions and peak periods were given.The study shows that the diffraction performance of the multi-directional wave is greater than that of the unidirectional wave in the model with dominant diffraction,therefore it is safer and more rational to take multi-directional waves to conduct the simulation.Besides,it also finds out that the terrain plays a significant role in wave diffraction.What’s more,it is safer to take unidirectional waves to perform the simulation in the model with dominant reflection,with the higher disturbance coefficient under unidirectional waves than that under multi-directional waves.