The invention provides a radioactive source on-line monitoring system based on an Internet of Things technology. The radioactive source on-line monitoring system comprises RF (radio frequency) cards, field monitoring terminals, a transmission network and an on-line monitoring informatization management platform, wherein the RF card is fixedly arranged in each monitoring site with a preset distance from a radiation source, unique identity information of a radiation source, approved geographical position information and the standard radiation dose rate are stored in the RF cards, each field monitoring terminal is arranged in the corresponding monitoring site, and comprises an RF card reader-writer, a radiation dose rate measuring instrument, video collecting equipment, a GPS (global positioning system) positioning device, a controller, an in-site warning device, a communication interface and a power supplying power supply, and the processor is respectively connected with the RF card reader-writer, the radiation dose rate measuring instrument, the video collecting equipment, the GPS positioning device, the field warning device, the communication interface and the power supplying power supply. The radioactive source on-line monitoring system has the advantages that the radiation source can be comprehensively monitored, then, through a communication network, the monitoring information can be remotely obtained in time, and the monitoring efficiency is effectively improved.