The micro-mechanical behaviors of fiber-concrete complexin the technology of distributed fiber optic sensor system for crackdetection were investigated. 3-D nonlinear numerical simulation wasperformed with ANSYS, considering the nonlinear interfaces of coating-sheathand sheath-concrete. The bilinear isotropic hardening model was applied forconcrete to relax local stress concentration and avoid excessive penetrationbetween the sheath and the concrete. The mechanical parameters of contactpairs were determined by tests. The microscopic stress distribution infiber-concrete complex and curvature distribution of fiber were obtained.The relationship between crack width and bending loss was analyzedquantitatively. The computational results have shown a good accordance withexperimental results. The influences of fiber layout and sheath thickness onsensing sensitivity and dynamic range have been proved theoretically.Meanwhile, an improved micromechanical analysis was developed for thetechnology of distributed fiber optic sensor system for crack detection.