For the relays protection and control system, a probabilistic graphical analysis technique (GO method) is introduced to quantify the reliability of the system protection based on the “three lines of defence”. According to the regional power grid security strategy and device configuration, a GO diagram of the signal flow of the system protection strategy is developed, the reliability analysis model algorithm is built. A new algorithm for dualised configuration simplification was proposed. The redundancy and reliability of the stability control scheme and device configuration are evaluated. The optimization strategy for the dual configuration of the system protection outlets is presented based on the results of the online and offline reliability analysis.