This study investigates the characteristics of the three-channel output interference signals from a fiber Mach-Zehnder interferometer based on a 3×3 coupler. The phase-fading problem is solved using a scheme that judges the positive and negative feedback based on the orthogonal signals. The LabVIEW software is used to realize the acquisition of orthogonal signals and the processing of feedback output signals. Measurement and analysis reveal that when the feedback signal is directly output, the interference signal briefly deviates from the stable point. The whole process requires approximately 35 ms. However, the proposed feedback-judgment scheme reduces the phase-stabilization time to approximately 18 ms. An optical-fiber collimation focusing system directs the light to the surface of the test object and receives the reflected light. A high-frequency (1.5 MHz) vibrational signal consistent with the input signal frequency is detected. The feasibility and effectiveness of the proposed feedback-judgment scheme and designed interference system are verified.