The invention provides an arc light online monitoring system based on the Internet of Things technology. The system comprises a monitoring center, a communication server, an acquirer and an arc lightsensor. The monitoring center provides a human-machine interactive platform and is used for carrying out parameter setting on the operated monitoring terminal and carrying out processing, storage, analysis and early warning on the data. The communication server is used for converting fiber signals or wireless signals into Ethernet signals, and forwarding data of the acquirer to the monitoring center. The acquirer is used for collecting data of the sensor, carrying out networking and transmitting arc light information to the communication server through the GPRS or the fiber. The arc light sensor is installed in an enclosed cabinet body and used for detecting ultraviolet spectrums in arc light and transmitting data to the acquirer through the fiber. According to the invention, flashover monitoring can be performed on outdoor ring main units and cable distribution boxes; monitoring conditions are reflected in real time; analysis and judgment are performed on fault pre-judgment and workers; and effective means are provided.