SWAN wave model have been widely used in wind wave hindcasting and forecasting. This study adopts SWAN wave model for wave simulation of Taiwan water. The simulation results show that the wave period estimations are always underestimated. In order to overcome this predicament, we change different kind of source terms and parameters involved in SWAN wave model. But it still can not obtain more precise results. With the further discussion we discovered the estimation of wave dissipation rate is unreasonable from SWAN model simulation. This is because the overall steepness involved in dissipation term. When wave energy distributed widely within frequency bands, the dissipation rates will be induced under or over estimated. This paper attempts to adopt a new dissipation formula based on individual steepness parameter into SWAN wave model.