The conductive fibers have great potential as flexible sensors. In our previous study, based on the experimental studies on sensing behavior of PPy (polypyrrole)-coated Lycra fibers, the mechanism of the strain sensing behavior was identified as open-close mechanism of the cracks on the coating layer when experiencing large deformation. In order to modeling its strain sensing behavior and describe quantitively the development of the micro-cracks, statistical analysis is conducted by image processing technique in MATLAB software. It was concluded that the variation of resistance is related to the micro parameters of the surface cracks, suck as the number, width and length of micro-cracks. These will be used in our further modeling work.