A method to improve the sensitivity of swept source optical coherence tomography (SSOCT) system is proposed. In the SSOCT system, when the splitting ratio of the coupler before the balanced detector, is not 50%∶50%, the DC bias in the detected interference signal will affect the sensitivity of the system. In this study, the influence of the splitting ratio of the coupler on the sensitivity is theoretically analyzed when the DC bias is introduced into interference signal, and it is proved that the sensitivity can be improved by the method of adjusting the splitting ratio and increasing the reference arm′s energy. Based on the parameters of the devices of the SSOCT system in the experiment, the sensitivity of the system is numerically simulated. The numerical simulation results prove the effectiveness of the proposed method, and the experimental results show that the sensitivity is improved by 2.3 dB after the proposed method is applied.