Abstract: A method to calculate the volume of oil/gas two-phase flow based on digital image process is researched. Noise reduction and strengthening pretreatment are taken on the image with digital image process to improve its quality. It uses edge inspection and image-completing method to calculate the distribution in water layer thickness along the pipeline, and fits the thickness distribution curves with least squares method. Geometric model is formed to calculate the phase volume of two-phase flow and water content is gained by numerical integration (the former integration can not obtain the solution). The analysis shows that the errors of image measurement in water content of oil/water two-phase rate are mainly contributed by three aspects in experimental environment, image process and model assumption. The experiment shows that the relative error between calculated and real values is not more than 10%. Therefore, the method can be used to inspect phase volume of oil/gas twophase flow for its higher precision.