For utilizing spectrum analysis to forecast the performance of ship in irregular waves, firstly estimate wave/wind spectrum density of voyage areas. Researchers proposed a variety of ocean wave spectrum expression based on a number of observational and theoretical work, for example Bretschneitder spectrum, Pierson-Moskowitz spectrum, ITTC parameter spectrum, JONSWAP spectrum, Torsethaugen spectrum. In this paper, a double-parameter spectrum method which is recommended by ITTC and ISSC is applied. This spectrum is applicable to full developed waves, developing waves and waves with swell