In　order　to　overcome　the　shortcomings　of　traditional　damage　test　and　detection　methods　in　terms　of　accuracy　and　practicability,　and　measure　the　cumulative　damage　of　beam　structure　due　to　fatigue　load　accurately　and　quickly,　the　method　to　extract　the　fracture　characteristics　and　dimension　of　cracks　on　key　parts　of　bridge　based　on　fractal　theory　and　image　processing　technology　is　proposed.　To　establish　the　functional　relationship　between　the　fractal　box　dimension　of　cracks　and　typical　mechanical　parameters,　the　fatigue　loading　test　of　T-type　RC　simple　sup-ported　beam　is　carried　out.　The　relationship　between　different　fatigue　loading　and　damage　states　is　established,　the　matching　relationship　between　the　fractal　dimension　and　the　damage　index　such　as　mid　span　deflection,　first　-order　frequency　and　static　and　dynamic　stiffness　is　clarified.　The　results　show　that　the　fractal　dimension　can　be　used　to　reveal　the　crack　development　and　structural　damage　evolution　process.　The　relationship　between　the　mechanical　parameters　and　the　fractal　dimension　is　obtained　by　establishing　the　precise　empirical　function　which　provides　a　new　idea　and　method　for　the　fine　evaluation　of　beam　damage　under　different　damage　states,　and　it　has　good　accuracy　and　robustness.　This　study　can　provide　strong　support　for　the　rapid　assessment　of　the　evaluate　beam　fatigue　damage　quickly　and　effectively.