The utility model aims to disclose an acousto-optic combined leakage monitoring system for a main steam pipeline of a nuclear power plant. The device comprises an acoustic emission leakage monitoringloop and a spectrum leakage monitoring loop, the signal input end of the acoustic emission leakage monitoring loop and the signal input end of the spectral leakage monitoring loop are respectively arranged at detection points of the main steam pipeline; the signal output end of the acoustic emission leakage monitoring loop and the signal output end of the spectrum leakage monitoring loop are in communication connection with each other through a network switch, and the network switch is sequentially connected with a control unit and a display unit. Compared with the prior art, through the combination of acoustic emission and spectroscopy, early warning is conducted before leakage of the main steam pipeline, the diversity and redundancy of the main steam pipeline leakage monitoring method are achieved, and the monitoring result is more credible; the monitoring sensitivity is higher, the response time is shorter, the reaction speed after leakage is found is remarkably increased, and larger safety margin is provided.