The invention discloses a spindle coaxiality detection mechanism, which is characterized in that the top of a base is fixedly provided with a mounting plate at one side, the top of the mounting plateis provided with a mounting slot, the mounting slot is internally provided with a horizontally placed rotating shaft, one end of the rotating shaft is provided with a driving motor, the rotating shaftis in threaded connection with a limiting plate, the top of the limiting plate is provided with a mounting base, the top of the mounting base is provided with a first arc-shaped block, the first arc-shaped block is fixed with a second arc-shaped block through fixing pieces, a spindle is fixed between the first arc-shaped block and the second arc-shaped block, the end, which is away from the mounting base, of the spindle is fixedly provided with a first bearing pedestal, the side, which is away from the rotating shaft, of the top of the base is provided with a dial indicator, the side, which is close to the first bearing pedestal, of the dial indicator is fixedly provided with a detection core rod, the detection core rod is screwed on the first bearing pedestal, the base is provided with acushion block, and the dial indicator is placed on the base. The spindle coaxiality detection mechanism is reasonable in design, convenient to operate, capable of realizing the detection for the coaxiality of an automatic lathe spindle and improving the spindle assembly quality, and easy to popularize.