A micro-mechanical modulator is designed based on the Michelson interferometer. In the experiment, the fiber signal is input from the input-sport and divided into two equal parts: the transmitted beam and the reflected beam, by beam-splitter. The modulating voltage signal is amplified and drives the piezoelectric ceramic pipe to do stretch oscittation in order to modulate the optical-path difference between the transmitted beam and the reflected beam. The transmitted beam and the reflected beam are interfered at the output-port and focused into fiber again. Then a modulated fiber signal is obtained. The modulator is operated for amplitude modulation. In the experiment, the modulation ratio is prior to 90%, signal-to-noise ratio is about 18 dB, and the bandwidth is also about 200 kHz. This device has the merit of high modulation ratio and low price, and can be applied as a modulator or chopper in optical signal transmission system.