This　paper　develops　a　state　transition　analytical　model　to　explore　the　endogenous　dynamic　law　of　supply　chain　and　interaction　of　its　endogenous　variables.　By　developing　a　differential　equation　system　for　this　model　and　applying　the　physical　phase　diagram,　we　attest　that　endogenous　factors　as　well　as　the　spontaneous　dynamic　law　in　a　supply　chain　will　determine　its　evolution　trajectory.　This　paper　also　reveals　that　the　initiatives　and　activeness　of　supply　chain　members　greatly　affect　supply　chain　system　evolution　and　their　effect　should　not　be　ignored　when　investigating　supply　chain　dynamics.