A novel Michelson interferometer fringe counter that can automatically adapt to different background light intensities is designed. The photodiode is used to convert the change of fringes into electrical signals and differential amplification with the output of the numerical control voltage divider circuit, and after being shaped by Schmitt trigger, it is sent to the single-chip microcomputer for counting and display. Experiments show that this counter can adapt to different background light intensity and light source light intensity, and has the advantages of high accuracy, easy operation and strong adaptability.