MIKE 21 BW model is used for analysis of the risk of long period wave inside the harbor basin.The model building uses white noise spectrum and natural wave as incipient wave.Based on the white noise simulation result,harbor resonance periods are calculated using digital filter technology.Based on the natural wave simulation result,the wave time series at the berth is extracted.And the long period wave is filtered using threshold of 30 seconds.Taking a harbor at west Africa as an example,the long wave risk of harbor basin is discussed,and the result can be treated as reference for harbor layout design.