Once the process-level network of smart substation fails, the secondary system function fails, the fault repair efficiency is low, and the reliability is reduced. In view of this, an approach for backup process-level network of smart substations based on the GOOSE feedback mechanism is proposed. First, according to requirements of the secondary system to process-level network transmission, quantitative models for interval jitter, frame loss rate and light power are established. Subsequently, single-index and integrated indices based starting criteria for backup optical fiber ports are put forward. Finally, the GOOSE feedback mechanism is used to realize the backup of main optical fiber ports. Simulation results show that the proposed method can quickly implement the switch of faulty optical fiber ports and improve the reliability of the process-level network.