Studying the structure evolution and mechanical properties of elastic polymers with strain has been difficult, however, these information have long been thought to be a key to understanding the structure-mechanical property relationships and will help guide the design of new materials for desired properties or uptake. In this work we show atomic force microscopy (AFM) nanomechanical mapping on the structural evolution and mechanical properties of the isoprene rubber (IR) with strain, and provide unique insights into the self-reinforcement mechanism. The highly deformed IR was composed of large amount of hierarchical nanofibers ranging from several nanometers of fibril crystallites to one hundred nanometers of fibers and being parallel to the stretching direction; that is, the highly deformed IR was fiberized. These hierarchical nanofibers are coupled to significantly enhanced the stress, indicating that the nanostructural characteristics consisting of fibril crystallites and oriented fiber bundles at multiple length scales is one of the key factors determining the self-reinforcement of IR, and likely most SIC elastomers.