A method of using polymer to encapsulate the bare FBG is proposed and implemented. The principle of the increasing in sensitivity of FBG is introduced, a novel packaging material composed of 100wt% unsaturated polyester, 2wt% Methyl Ethyl Ketone Peroxide and 2wt% cobalt naphthenate is realized. With the help of casting a model, FBG is encapsulated. After establishing the experimental platform, the temperature sensitivity of the packaged FBG is also analyzed. The comparison of the experimental results between the packaged FBG and the bare FBG shows that over the temperature of 24-44℃, the equivalent temperature sensitivity of the packaged FBG is 0.10387nm/℃, which can be increased by about 14.268 times as much as that of bare FBG and close to the theoretical values 0.108nm/℃. The FBG package material and technique is effective in the increasing of the temperature sensitivity, which is suitable for applications where wavelength references for FBG sensor system with high temperature sensitivity is required, especially in the measurement of human body temperature.