The invention discloses a temperature measuring nut, system and method used for ring main unit temperature monitoring. The temperature measuring nut includes a nut and a temperature measuring unit. Afirst ultra-high frequency antenna of the temperature measuring unit is connected with an ultra-high frequency DC converter, an ultra-high frequency command signal conditioning unit and an ultra-highfrequency data signal conditioning unit separately through signal lines. The ultra-high frequency DC converter is connected with a radio frequency label chip and a DC-DC converter separately through power lines. The DC-DC converter is connected with a temperature sensor through a power line. The radio frequency label chip is connected with the ultra-high frequency command signal conditioning unit,the ultra-high frequency data signal conditioning unit and the temperature sensor separately through signal lines. According to the invention, the temperature measuring unit is arranged in the temperature measuring nut, so that no external space occupancy is caused and the temperature measuring nut is suitable of being arranged in a large scale in a ring main unit equipment.