The utility model relates to an axial clearance measuring device comprising a sleeve and a rotating shaft which can be flexibly arranged in the sleeve along an axial direction. The rotating shaft is provided with a threaded segment which is constructed in the first end part area of the rotating shaft, and an expansion segment which is constructed in the second end part area of the rotating shaft. The sleeve comprises a connecting end which can be flexibly matched with the threaded segment, and a bulging end which encloses the expansion segment. The maximum external diameter of the expansion segment is greater than the minimum internal diameter of the bulging end. The external wall of the expansion segment and the internal wall of the bulging end can be extruded with each other so that the bulging end can be bulged. With application of the axial clearance measuring device, axial clearance between the shell of a differential mechanism and a supporting conical gear arranged in the internal part of the differential mechanism can be detected more accurately, conveniently and rapidly.