Abstract: The Hilbert-Huang transform(HHT) was used to analyze the differential fluctuation signal of gas-liquid two-phase flow in a horizontal pipeline. By using the empirical mode decomposition(EMD) method, the signal was decomposed into a finite and small number of intrinsic mode function(IMF), and then the Hilbert transform was applied to each of these intrinsic mode functions to get the energy-frequency-time distribution, designated as the Hilbert spectrum. The energy characteristics of different intrinsic mode functions was extracted to characterize the differential pressure fluctuation signal. Based on the above analysis, a comparison of the results for different diameters of pipeline was presented and the relationship between the energy distribution of signals of different frequency bands and flow pattern conversion was analysed. Meanwhile, the differences between the wavelet method and HHT method were also discussed. The experimental results show that the HHT is an extremely powerful tool for the analysis of nonlinear and non-stationary signals，and the extracted energy characteristics can reflect the flow state of gas-liquid two-phase flow and flow pattern conversion.This method could be useful for the signal analysis in gas-liquid two-phase flow in a horizontal pipeline.