The Direction-judgable Fiber Displacement Interferometer (DJFDI) was proposed on the basis of optical Doppler effect and heterodyne technique. The proposed interfermeter was assembled by using the components well developed in the telecommunication industry, which consisted of a fiber-pigtail semiconductor laser, a 1×2 fiber coupler, a three-port optical circulator, a fiber probe, a 3×3 fiber coupler, a detector, an oscilloscope, and so on. Based on above original configuration, EDFA was utilized in DJFDI to enhance the signal power. The signal processing method based on Lissajous figure was brought forward. The vibration of piezoelectric ceramic vibration was measured to study its measurement capability of micro-displacement and the influencing factors. The experimental results show that the dominant influencing factor is nonideality of 3×3 fiber coupler, such as instability of the output phase difference of the DJFDI’s interference signals.