Laser Doppler vibration measuring system has been widely used in many fields, in order to eliminate the phase fading,
phase generated carrier (PGC) homodyne demodulation technology has been applied usually, and dual-optical-channel
balanced detection technology has been used to suppress the intensity noise of the light source. However, theoretical
analysis reveals that the intensity noise of the light source cannot be eliminate totally due to the modulation, which is still
the main noise in the system. In this paper, we consider the influence of the intensity noise of the light source and the
shot noise of the detectors. By numerical simulating, we analyze the origin of the noise, especially the influence of
remnant intensity noise to signal-to-noise ratio of the system, and find the optimal parameters of the system.