To improve the sensing characteristics of a Fiber Bragg grating(FBG) temperature sensor with a Ni coating , the causes of the hysteresis error and the difference of sensitivities when it was heated and cooled were researched. Results indicate that the residual stress induced by electroless-electroplating makes the sensor imprecise. The mechanism of the residual stress was discussed, then a heat treatment method was proposed for the metallized FBG(MFBG) with a nickel coating. In treatment, the MFBG sensor was put in a drying oven at 120 ℃ for 8 hours three times,and every time it was cooled with the oven. A comparison experiment for the MFBG with the nickel coating was performed in 100-300 ℃,results show that the hysteresis error of the sensor is 6.64%, and the difference of sensitivities when it is heated and cooled is more significant before the heat treatment. The sensor characteristics are not be amended even if it is performed temperature cycle again after half a month. However, the hysteresis error of the sensor is descended to 3.62%, and the sensitivities of the MFBG when it is heated and cooled are 22.84 pm/℃ and 22.76 pm/℃,respectively, after the heat treatment. The experiments demonstrate that with a higher sensing accuracy, the working range of the MFBG with the nickel coating has expanded to 300℃ after effective heat treatment.