The invention discloses a unified power flow controller (UPFC)-based overload control method of a power transmission line. The UPFC-based overload control method comprises the steps of firstly, determining a bus set which is monitored and protected by calculating sensitivity of current amplitude of each power transmission line in a power grid on change of an active power flow set value of a UPFC; and secondly, monitoring the current amplitude of the power transmission line in the set during the running process of the power grid, wherein the active power flow set value of the UPFC can be automatically adjusted by a control strategy so that a load of the power transmission line is controlled to be within a safe and stable running range when overload of the power transmission line is monitored. By the circuit overload control strategy, the problem of overload of the power transmission line brought by a fault or load/power generation fluctuation can be automatically solved, the safe running of the power transmission line is ensured, and the overload control method is very necessary for improvement of the running flexibility of a system and the safety of a power system and has important significance to engineering application of the UPFC and safe and stable running of the power grid.