The utility model discloses a thermal resistor. The thermal resistor is applicable to measuring the temperatures of a bearing bush and oil, is installed with a fixed screw thread, and comprises a temperature sensor and a built-in temperature transmitter, wherein a radiator is arranged between the temperature sensor and the temperature transmitter. The temperature transmitter is completely sealed in a protection tube through an epoxy resin; and the thermal resistor adopts a Hersman joint as a field connection terminal. The thermal resistor is installed by a fixed screw thread and is stable and reliable in structure; the arrangement of the radiator can prevent the built-in temperature transmitter against thermal damages during heat conduction; the temperature transmitter is sealed by the epoxy resin in the temperature protection tube to isolate air and external pollution so as to prolong the service life of the temperature transmitter; the Hersman joint is taken as the field connection terminal, the dustproof and flameproof performances are good, and different specifications of electrical interfaces can be selected to provide convenience for use.