Abstract: During certain times, pre-stress that pre-blast hole produced to neighboring hole can control form of original crack in the fixed point and fixed direction, and it can consider blasted medium as uniformity of continuity and discontinuity body. Pre-split gap formed principle is researched using blasting mechanics and fracture mechanics. And the main parameters of pre-split blast's calculation formula are derived.

Key words: Pre-split, Theory of gap-formation, Initial gap, Parameter calculation