In this paper, a multiple cracks monitoring system composed of a fiber optics cable and an interrogation unit based on Optical Backscattering Reflectometry technique is demonstrated. A mechanical strain transfer model is validated by performing an experimental test on a real scale reinforced concrete beam. The model is fitted to the strain spatial distributions, and the resulting parameters are discussed. Estimated crack openings are compared to those measured using traditional LVDT sensors and Digital Image Correlation (DIC) technique. Results show that this system, initially a strain monitoring system, can efficiently detect all multiple cracks, follow its propagation inside the structure, and more importantly monitor the surface and in-depth crack openings. The proposed multiple crack monitoring system will be of great help for early crack detection, as well as monitoring long-term degradation phenomenon like fatigue.