In　order　to　study　the　optimal　delay　time　of　inter　blasthole　of　millisecond　blasting,　which　is　calculated　through　stress　wave　and　explosive　gas　energy,　an　detonation　gas　motion　equation　and　a　dynamic　equation　are　proposed,　which　is　consisted　of　detonation　gas　destruction　scope,　time,　and　the　mathematical　model　of　velocity.　Specifically,　many　theories,　such　as　rock　broken　theory,　wave　theory,　theory　of　fracture　mechanics,　thermodynamics　theory　and　theory　of　fracture　mechanics　are　utilized　during　formula　derivation.　Moreover,　after　correcting　the　semi-empirical　formula　from　previous　study,　a　theoretical　model　of　millisecond　blasting＇s　delay　time　is　established.　As　a　result,　the　calculated　optimal　delay　time　is　25　ms　after　inserting　the　rock　mechanical　properties.　By　contrast,　the　experiment　of　delayed-detonation　combination　in　different　period,　reveals　that　the　optimal　delay　time　is　24　ms,　which　is　consistent　with　the　theoretical　result.　©　2017,　Editorial　Board　of　Journal　of　Harbin　Institute　of　Technology.　All　right　reserved.