Nonperiodic cycle detection methods for gas/liquid two phase flow system were discussed. Cycle detection methods, such as Hurst analysis, the V statistic and the P statistic were briefly reviewed; in addition, a modified P statistic method was introduced. Two types of time series, i.e. mathematically sine wave time series and experimental electrical capacitance tomography time series of plug flow and slug flow under different flow conditions were investigated to verify the effectiveness of different cycle detection methods. The sine wave time series and sine wave time series under gauss noise were used to validate different cycle detection methods. For the electrical capacitance tomography time series of different flow regime, discrete wavelet transform (DWT) was adopted to decompose the original signal into approximate signal and detail signals, and then different cycle detection methods were mainly applied to realize cyclic characterization analysis of detail signals for plug flow and slug flow. The results show that the nonperiodic cycle characteristic analysis can reflect the property of different flow regimes.