The main objective of this research is to determine the influence of micro-crack on the propagation of a semi-infinite crack. This study is mainly based on the determination of the strain energy during the interaction between the semi-infinite crack and the neighboring microcrack. The problem is formulated by a plane element, having a micro-crack varies around itself and around a semi-infinite crack. The cracked element is subjected to a uniform load according to mode I. The theoretical analysis of the strain energy is based on the stress found during the propagation of the semi-infinite crack. During the positioning of the micro-crack with respect to the semi-infinite crack, according to the strain energy results, the presence of the micro-crack can amplify, reduce and sometimes arrest the propagation of the semi-infinite crack.