Abstract: To overcome the difficulty in the detection of cracks in concrete, distributed optical fiber sensors can be pre-embedded in structures. Based on the principle of crack detection using distributed optical fiber sensing technique, the layout of optical fiber was discussed, the relationship between light attenuation and crack width was investigated through tests in laboratory, and a semi- empirical formula for light attenuation and crack width was obtained. In addition, the measures of optical fiber sensor protecting in construction and their long-term stability and reliability in structures were discussed.