The invention provides a reliability monitoring system of a power transmission line applied to a smart grid. The system comprises: a collection module arranged onsite and used for collecting image information of the monitored power transmission line and transmitting a collected power transmission line image to a monitoring center in real time; and the monitoring center used for receiving the powertransmission line image sent by the collection module, performing analysis processing on the image information to extract a contour of the power transmission line in the power transmission line imageand all foreign matter contours near the power transmission line, comparing the contour of the power transmission line and all foreign matter contours with a pre-stored power transmission line contour template and an electrical component contour template to judge whether a foreign matter exists around the power transmission line, and sending early warning information when discovering the foreignmatter. The reliability monitoring system provided by the invention analyzes the reliability of the power transmission line according to the image information of the power transmission line, so that the intelligence level is high, the operation is simple, no manual participation is required, the implementation property is high, no influence is generated by external factors such as weather, the workload of the operation and maintenance personnel is reduced, and the accuracy is high.