SERS technique has become one of the powerful tools for monitoring surface/interface reaction processes due to its extremely high surface sensitivity and selectivity. The control of photocatalytic performance is critically based on the well understanding of the reaction process at molecular level. The in-situ monitoring of photocatalytic processes can be realized by the integration of SERS substrate and photocatalyst to provide the interfacial information. In this paper, bifunctional Cu2O-Au composites with both catalytic and SERS activities were synthesized, the SERS enhancement and photocatalytic degradation of methyl orange (MO) were studied as well as the dynamic processes of photocatalytic degradation of MO. The results demonstrate that bifunctional Cu2O-Au composites is beneficial to effectively integrate SERS effect and photocatalytic performance, and the in-situ monitoring of photocatalytic degradation at the Cu2O-Au interfaces was achieved accordingly. The introduction of Au nanoparticles enhanced the SERS effect by two orders of magnitude and double the catalytic degradation performance of Cu2O. In situ monitoring results of MO photocatalytic degradation processes revealed that N=N bond was the most easy to break, and C=C bond was the most difficult to break. The sequence of chemical bond break is N=N > Ph1-N=,= N-Ph2, and Ph1-N=, C-N > Ph-N.