Abstract: A spatial phase modulation laser interferometer for glass thickness measurement is designed. The interferometer was mainly composed of a vertical cavity surface emitting laser (VCSEL), a single mode fiber and a linear array charge coupled device (CCD). The reflected lights from the two surfaces of the glass produced two-beam interference. The generated spatial phase modulated interference image was detected by the CCD. The spatial frequency of the image was proportional to the thickness of the glass. The thickness measurement resolution could reach the nanometer level. The glass thickness measuring experimental device has advantages such as small volume and low cost. It involves optical interference, laser principle, photoelectric detection, field programmable gate array (FPGA), electronic circuit, virtual instrument, digital signal processing. It is suitable for teaching experiments of senior undergraduates.