Abstract: During the development of the solar panel substrate, the performance of the substrate needs to be tested. Commonly, the coupon is made and the stiffness of the coupon is tested by the three-point bending method. But the result may be influenced by external factors during the coupon preparation and the stiffness measurement, and therefore might not truly reflect the substrate's real performance. In this paper, the stiffness of the substrate is obtained by the vibration test, and the test result shows that the deviation between the actual stiffness and the numerical result is only 2.2%. Compared with the result of the three point bending test, the vibration test result reflects better the real performance of the substrate.