In order to improve the strain measurement precision of fiber Bragg grating (FBG) sensors, a strain calibration method was presented according to the engineering application of FBG. The strain sensitivity coefficients of packing FBG were determined using theoretical analysis and experiments. Then, the difference of the strain sensitivity coefficients between the theory and experiments was analyzed. The results show that the proposed method was accessible and effective. It can also be applied before the FBG strain measurement to improve precision and accuracy.