Stress produced in metallization of fiber Bragg grating (FBG) using electroless-electroplating method affects the sensing accuracy of FBG directly. Based on the mechanism of stresses, the changes of FBG′s transmission spectrum in metallization are studied for better sensing accuracy. Experiments show that electroless plated FBG exhibits broadened spectrum and reduced peak value. Theory and simulation analyses are conducted to study the stress in electroless plating. Results show that the thermal stress causes perturbation in FBG. Prolonging the cooling time is used to reduce the thermal stress. And during the electroless plating, the solution is mixed timely to make the stress uniform. It is shown that stress in electroless plating with the optimal condition affects the FBG little. The following electroplating experiments show that most stress is produced in the electroplating process. The changes of FBG′s spectrum are minimized by stabilizing higher electroplating temperature, mixing timely and using double electrodes. Finally, temperature sensor experiments for the metal coated FBG (MFBG) metalized under the optimized condition prove that the hysterisis error is reduced compared with the reported results.