The utility model discloses an online temperature measurement and alarm device of a transformer substation high-tension switch cabinet, and solves the problems that existing switch cabinets are not accurate in temperature measurement and not timely in monitoring and alarming. The online temperature measurement and alarm device of the transformer substation high-tension switch cabinet comprises a transformer substation switch cabinet (1) and a fiber Bragg grating (FBG) temperature on-line detector (5), wherein a FBG temperature sensor (3) is arranged on a connecting portion (2) of a switch contact in the transformer substation switch cabinet (1) and a busbar, the FBG temperature sensor (3) is connected with the FBG temperature on-line detector (5) arranged outside the transformer substation switch cabinet (1) through optical fibers (4), and a prober capable of analyzing emitted broad-band light and narrow-band light returned by the FBG temperature sensor (3) is disposed in the FBG temperature on-line detector (5). The online temperature measurement and alarm device of the transformer substation high-tension switch cabinet achieves real-time monitoring of a high-tension switch cabinet, centralized control and accurate location and alarm.