Owing to Micro-mechanical silicon membrane structures micro size and fragile properties, the method to determine Young′s moduli must be non-contact and nondestructive. Based on the photo-thermal effect, a novel method was presented by using optically excited resonance and optical fiber sensing techniques in this paper. This new method utilizes first three resonant modes of the fabricated silicon membranes to get a more accurate evaluation of Young′s moduli, and a novel optical exciting and sensing system using only one optical resource was set up to make the evaluation more practical.