This article describes the generation methods of irregular sea waves specified by its spectrum. It will describe the difference between the small equal frequency division method and the energy equivalence frequency division method. In the latter method, it is shown to completely generate a stationary irregular wave in an engineering regard. The theoretical iteration period of the time histories generated by the method is also obtained by using a symbolic computation. Finally, experimental results of the generation of sea waves spectra are presented. The spectrum of the revolution of the AC servomotor driven by the energy equivalence frequency division method is obtained. The good agreement between the measured and calculated spectra is shown.