The utility model relates to an optical-sensor-based insulator filthiness on-line monitoring system comprising an optical sensor, an insulating protective module, a photoelectric conversion module, a data acquisition module, a master control module, a communication module and a power supply system, wherein an output end of the optical sensor is connected with an input end of the insulating protective module, an output end of the insulating protective module is connected with an input end of the photoelectric conversion module, an output end of the photoelectric conversion module is connected with an input end of the data acquisition module, an output end of the data acquisition module is connected with an input end of the master control module, and an output end of the master control module is connected with an input end of the communication module; the power supply system is electrically connected to the optical sensor, the isolating protective module, the photoelectric conversion module, the data acquisition module, the master control module and the communication module. On-line monitoring operation is performed through use of data communication technologies, insulator filthiness detection can be realized without power cut, insulator filthiness condition can be effectively grasped, good real-time performance is realized, and normal and safe operation of a power grid cannot be affected. The optical-sensor-based insulator filthiness on-line monitoring system which is free from environment interference is high in accuracy and stable in on-line real time monitoring operation.