The way of computing the cyclic cumulant of cyclostationary signal of unknown cyclic frequency is studied, the nth-order lag product of the input cyclostationary signal is analyzed and the way of decreasing the used EMS memory and the time of compute is studied. By the analysis of simulation testing data of phase modulation signal, the cyclic bispectrum is showed to be effective. And the cyclic bispectrum is used to analysis of the industrial vibration data of the rotating machine and proves to be effective.