The purpose of this study is to quantitatively assess the effect of uncertainties on the wave forecasts using the ensemble approach. The ensemble method is an effective approach to assess the effect of the model uncertainty by producing not only one, but several forecasts. The ensemble wave modelling system was applied to the Taiwan sea area, especially for typhoon wave. There are four different operational atmospheric models that provide predictions of wind at 10 m height above sea surface. The simulated wave of WAVEWATCH III drove from NCEP, JMA, NFS, and WRF wind fields. From the simulated wave heights of all ensemble members, it can be clearly seen that the uncertainties from the atmospheric predictions have significantly affected the predicted hydrodynamic results. A further ensemble statistics, including the ensemble mean, and mean ± standard deviation. The measurement outcome scatters in between wave forecasting of mean + standard deviation and mean - standard deviation, which proves that the ensemble forecasting is able to reasonably predict typhoon waves. Therefore, the accuracy of the predictions of waves can be significantly improved by using ensemble approach closer to the observed wave measurement.