In the multi-user optical code division multiple access (OCDMA) transmission system, multi-user interference (MAI) seriously affects the transmission performance of the system. In view of the fact that the multi-user interference comes from the incomplete orthogonality of codewords, the received signal and the system damage can be expressed by the autocorrelation and the cross-correlation functions of codewords. A new research idea regarding the multi-user interference as the effective information that can be reconstructed is introduced to suppress the multi-user interference, and a serial feedback interference suppression algorithm based on the digital signal processing technology is proposed. A simulation platform for two users synchronous access spectrum amplitude code optical code division multiple access (SAC-OCDMA) transmission system is built to verify the effectiveness of the algorithm in suppressing the multi-user interference. The simulation results show that compared with the optical threshold device, the serial feedback interference suppression algorithm can suppress the multi-user interference better, the improvement of the system transmission performance is greater, while the power penalty introduced is only 2.3 dB.