Blech critical product (BCP) is the product of the metal strip length times its current density passing through, and has served as the threshold for electromigration occurrence. The validity of BCP is still under debates. In this study, we employed in situ synchrotron radiation-based X-ray diffraction, ex situ scanning electron microscopic and transmission electron microscopic analyses to revisit BCP for aluminum strip. We proposed a new mechanism based on electric current-dislocation interaction and stress relaxation to revisit the BCP mechanism. The abnormal microstructures from microscopic analysis support the perspective where a series of complicated defect dynamics process involved in stress relaxation including recovery, recrystallization and grain growth.