The invention discloses an online monitoring system of cable connector temperature rise. The system comprises a phase-A buried temperature-measuring sensor, a phase-B buried temperature-measuring sensor, a phase-C buried temperature-measuring sensor, a central collector and a cloud server monitoring center. The phase-A buried temperature-measuring sensor, the phase-B buried temperature-measuring sensor and the phase-C buried temperature-measuring sensor are all connected with the central collector through fibers, allowing data communication; data is transmitted between the central collector and the cloud server monitoring center in a wired or wireless manner. The system has the advantages that according to the actual conditions of cable connectors in China, the buried temperature-measuring sensors are adopted, the principle of capacitive coupling power taking is utilized, online monitoring of cable connector temperature rise is achieved by means of the fiber-optic communication technique, and the system is significant to the improvement of cable connector health level and the guarantee of running safety of a power system.