The invention relates to a method for obtaining water saturation of a compact sandstone wax-sealed rock core, which belongs to the field of petroleum exploitation. The method is characterized in thatreal drilling mud is added in a pressure tank on ground, a colored ink used for indentifying the colors is added in the drilling mud, a force pump is used for adding nitrogen in the pressure tank so that the pressure in the pressure tank is kept at preset pressure, then the pressure in the pressure tank is kept for a while, a process that a mud filtrate is intruded into the rock core during a drilling well rock core-taking process is accurately simulated, and the depth that a mud filtrate is intruded into the rock core can be conveniently observed through the color, so that preparation is madefor determining original water saturation of an extra-low permeability and compact sandstone gas layer of the rock core which is not invaded by the mud filtrate during a subsequent rock sample-drilling process. A wax-sealed full-diameter compact sandstone rock core sample is used for substituting the sealed rock core-taking full-diameter compact sandstone rock core sample, and the determination cost of the low permeability and compact sandstone gas layer water saturation is greatly reduced.