We present a simple but effective method for measuring small angular displacement based on a scanning Twyman interferometer ,in which, one of the two mirrors is mounted on the piezoelectric ceramic (PZT) droved by saw-tooth voltage, the status of interference fringes changes from static to dynamic. A photoelectric detector detects this dynamic photo-signal and changes into electronic signal. The signal is inputted into an oscillograph. The oscillogram will present interference crests. The method for measuring small angular displacement is based on the linear relation between the angular displacement and the crest shift on the oscillogram.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.