The balanced detection system based on Mach-Zehnder type interferometer is applied to increase the detection sensitivity in laser Doppler velometer experimental system. Based on the Doppler effect, the principle of laser velometer system and the balanced detection realization method are described, the formula of light current is derived, and its advantages compared with the conventional coherent detection technique are analyzed. The formula of the signal-to-noise, which is derived by light current, is used to attain the influence factors. The simulation results demonstrate that when the reflection coefficient is set in (0.2908,0.7092) or the conversion coefficient ratio of two detectors is set in (0.4632,1), the dual balanced detection technique offers higher signal- to- noise ratio than the conventional detection technique. The sensitivity of the Doppler velometer system is strengthened with balanced detection technique.