The present invention provides a closing failure protection method for the series transformer bypass switch of a unified power flow controller (UPFC). According to the technical scheme of the invention, the method is composed of four types of equipment, namely a UPFC value control protection device, a series transformer non-electrical-quantity protection device and a body non-electrical-quantity relay, a series transformer electrical-quantity protection device, and a series transformer bypass switch. The closing failure protection for the series transformer bypass switch is implemented by the series transformer electrical-quantity protection device. The series transformer electrical-quantity protection device receives signals sent from other protection devices, acquires the location information of the series transformer bypass switch and adopts the information as a criterion for judging the closing failure protection action of the series transformer bypass switch. In this way, the closing failure protection for the series transformer bypass switch of the unified power flow controller (UPFC) can be realized.