In this paper, an efficient method of suppressing interference is presented in an optical feedback-cavity enhanced absorption spectroscopy (OF-CEAS) system. The Ariy function is used to analyze the interference signal in the transmission cavity mode signal. It is found that the interference signal in system originates from multiple reflections of the beam in the mirror, which is verified by replacing three kinds of cavity front mirrors with different thickness values. The result obtained by the Ariy function is used as a background signal, and the absorption spectrum signal can be obtained by making its difference from the absorption signal of the measured gas. This method effectively avoids the frequency error caused by the inability to measure the background signal and the absorption signal at the same time in the OF-CEAS system. Finally, the absorption characteristics of acetylene gas at 1.53 μm are measured. Based on the signal-to-noise ratio, the detection sensitivity of the system is evaluated to be 7.143 × 10^–8 (1σ). Experiments show that this method is effective in improving the detection sensitivity of OF-CEAS system.