Mathematical model of signal-to-noise ratio (SNR) for balanced coherent system is proposed and SNR of balanced coherent system is simulated analytically with that of conventional coherent system. Simulation results show that SNR of balanced coherent system is symmetrical with 0.5 beam splitter coefficient with the matched detectors. Whereas, the optimum beam splitter coefficient for maximum of SNR is deviated from 0.5 with the unmatched detectors. Experimental configuration for 2 μm balanced coherent detection is demonstrated in which the SNR is more than 19 dB higher than that of conventional coherent system with 0.5 beam-splitter coefficient and the range for SNR of balanced coherent detection near to saturation is more than 0.2 wider than that of conventional coherent system under the same optical power condition.