Tropical cyclone "Gavin" caused extremely high wave situation in Funafuti atoll, Tuvalu on March 1997. Although the extremely high waves due to tropical cyclones caused large morphological changes on atoll islands, the detail of the waves under tropical cyclones are not fully understood, because such strong tropical cyclones attack atoll islands once in a few decades. In this study, the numerical simulation of winds and waves under the tropical cyclone "Gavin" were carried out. The simulated results showed that the lagoonal significant wave height increased twice as high as the mean wave height in March. In the tropical cyclone situation, the place of passage and effective fetch are important for the lagoonal wave condition.