A new way to measure fibers’valid elastic2op tic constant is presented which based on op tical fiber Bragg grating sensor. The method caters for the need of measuring new-style fibers’valid elastic-optic constants presently.The constant ismeasured by a temperature referrence gratin, a measuremental grating and one material known of expansion coefficient, combiningwith the characteristic of fiberBragg grating. Experimental setup andmeasurement princip le are discussed. The result of experiment proves that the system can solve the existent cross sensitive problem which caused by temperature and the strain effectively. So we can measure the fiber’s valid elastic-op tic constants successfully, and the result ofmeasurement proves that the error is smaller than 1. 3%.