An optical fiber temperature sensor used for an oil-immersed transformer winding is characterized in that the optical fiber temperature sensor is composed of two protective tubes, two fixing caps and a transmission optical fiber; a fiber grating is arranged in the transmission optical fiber, and the two protective tubes are connected with the two fixing caps respectively; the two protective tubes are hollow, one of the fixing caps is equipped with a central through hole, and the other fixing cap is equipped with a groove; the transmission optical fiber penetrates from the central through hole of one protective tube, then penetrates the central through hole of one fixing cap to enter in the other one protective tube, and then enters in the other fixing cap via the groove connecting the protective tube and the other fixing cap. All parts are connected via one or the combination of the mechanical connection, the bonding agent connection and the welding connection. The advantage of the utility model is that the optical fiber temperature sensor used for the oil-immersed transformer winding is simple in package, convenient in installation and interchange, has no error, has no temperature drift during the long-term running process, and does not need to be calibrated again.