Abstract: The volume ratio between vapor and liquid of hydrocarbon inclusions is an important parameter for PVT simulation. Moreover, the judgment of the boundary between vapor and liquid is very important for the accuracy of the vapor/liquid ratios. A method for accurately determining the volume of hydrocarbon inclusion has been developed in this study. High resolution Laser Confocal Scanning Microscopy was used to obtain three-dimensional images of hydrocarbon inclusions. The liquid phase boundary was determined by three-direction coordinates under transmission light and fluorescence. 3DforLSM software was used to calculate the liquid phase volumes of hydrocarbon inclusions. Line scan was carried out across the vapor and liquid boundary using Laser Confocal Fluorescence Microscopy, in order to determine the vapor phase boundary according to the change of fluorescence intensity. The average of the results from multiple scans was used as the diameter of the vapor phase. This method avoids the error of manual judgment of the vapor and liquid boundary with a precision of 0.02 μm. The method improved the analytical precision of vapor/liquid ratios and allows for more reliable reconstruction of the trapping pressure by hydrocarbon inclusions.