Abstract: The flood discharge alarm system serves as a core early-warning facility to protect personnel and facilities along downstream river channels during flood discharge dispatching of hydropower stations. Its timeliness of early warning and standardized operation procedures directly affect the safety management of flood discharge operations. Aiming at the drawbacks of the original flood discharge alarm system at Haokou Hydropower Station., including only local manual operation in the central control room, low automation level, and artificial reliance for early warning sequence control, this paper proposes a remote control retrofit scheme based on the common local control unit (LCU) of the power station. By adding a three-position authority switching circuit, establishing hierarchical sequence control logic in PLC, and upgrading the upper computer monitoring configuration synchronously, the scheme realizes three core functions: remote and local manual start/stop of flood discharge alarm, 10-second pre-warning before unit startup, and multi-interval hierarchical automatic early warning prior to flood discharge. Field tests verify that the retrofitted system features reliable logic, complete authority interlock and standardized controllable early warning procedures. It effectively improves the emergency response efficiency and operation automation level of flood discharge early warning, and provides replicable engineering practice references for intelligent upgrading of flood discharge alarm systems in similar small and medium-sized hydropower stations.