Abstract: In this paper, a study on the characteristic of flow regime for oil-gas-water multiphase flow in horizontal pipeline has been made taken oil, gas and water as testing medium. The pressure drop fluctuation signals of oil-gas-water multiphase flow in horizontal test section have been measured. The diffusion analysis methods are proposed to analyze the pressure fluctuation signals. It has shown that results are found distinct quantity characteristic of the signals corresponding to different multiphase flow regimes. The results implicate the system of multiphase flow regimes. Therefore, the diffusion method may be adopted to identify the flow regime. Owing to the experiment, the method is very effective and easy to write a simple code for the on-line analysis.