Abstract: The activity measurement of ⁸⁸Y by 4π(PPC)X-γ digital coincidence counting method was introduced in this paper. In order to improve detection efficiency of X ray, high pressure proportional counter was used. It is found that the argon methane gas has the advantage of high detection efficiency and low operating voltage by comparing the plateau curves of methane gas and argon methane gas. The argon methane gas is chosen as the working gas. After the collection of original spectrum, different γ windows were selected for the offline digital coincidence counting calculation, and the efficiency extrapolation values and the measurement uncertainty were analyzed.