The maximum wave height is significantly important for the prevention of coastal and marine disaster as well as for the calculation of design wave.The maximum wave height formula based on the Rayleigh distribution can not reflect the influence caused by spectral width.Thus,the theoretical value of maximum wave height obtained by that formula is higher than the real value in practice.Through analyzing the 10-years’measured data of Norwegian Sea,we find that Hmax/Hs decreases gradually with the increase of spectral width.A maximum wave height formula with spectral width as an influence factor is deduced,which is easily to use and has good practicality.