Abstract: The interfacial strain distribution and changing patterns are directly measured in the process when the steel fiber is pulled out from the concrete matrix using Digital Image Correlation Method (DICM) and single fiber pull-out test. Meanwhile, the real-time process of bonding, debonding and displacing is observed. The results of the experiment show that the microscopic strain localization leads to the localization of the fiber’s interfacial shear failure. This kind of strain localization is characterized by alternating occurrence, development and transference of the interfacial debonding failure at an apparent and regular interval both in time and space. The test and analytic results show that the DICM provides a new approach to studying and measuring the interfacial mechanical behavior of the fiber composite.