In order to increase the signal-to-noise ratio (SNR) and improve the detection sensitivity of the optical coherence tomographic (OCT) system, the main noise sources in the OCT system are analyzed in detail. A theoretical noise model is then proposed which may be used to analyze the effect of different parts of OCT system. Based on the theoretical results, the performance of an OCT imaging system is analyzed. Through measuring the noise level of the system, the experimental model of the system noise is obtained, and then it is used to correct the theoretical analysis results. Based on the above analysis, the imaging performance of the OCT device is optimized. The axial resolution of 16 μm, and the detection sensitivity of -90 dB have been obtained.