An　improved　PID　control　excitation　regulator　with　high　reliability　based　on　OPC(OLE　for　Process　Control)　is　introduced　for　synchronous　generator,　in　which　the　PLC(Programmable　Logic　Controller)　is　taken　as　the　main　controller　and　the　extended　Ethernet　network　module　is　used　for　OPC　data　exchange　with　monitoring　computer.　Cooperated　with　the　peripheral　IC　chips,　it　realizes　the　frequency　measuring　and　synchronization　trigger　signal　generation.　The　use　of　improved　PID　controller　with　adaptive　parameters　enhances　its　robusticity.　The　interfacing　circuit　between　PLC　and　peripherals,　the　control　of　generator　startup　and　shutdown,　the　limiting　protection　of　excitation,　the　improved　PID　control　and　the　OPC　communication　are　introduced　in　detail.　Its　application　in　hydropower　plant　shows　that　the　designed　regulator　has　more　functions,　higher　reliability　and　better　static　and　dynamic　performances.