To　address　the　shortcomings　of　traditional　damage　test　and　detection　methods　in　terms　of　accuracy　and　practicability,　the　fracture　characteristics　and　dimension　extractions　of　cracks　on　key　parts　of　bridge　based　on　fractal　theory　and　image　processing　technology　is　proposed.　By　establishing　the　functional　relationship　between　the　fractal　box　dimension　of　cracks　and　typical　mechanical　parameters,　the　rapid　and　accurate　damage　assessment　can　be　achieved.　In　order　to　verify　the　effectiveness　of　this　method,　the　fatigue　loading　test　of　T-type　reinforced　concrete　simple　supported　beam　was　carried　out.　The　fractal　theory　is　used　to　establish　the　function　between　the　fracture　fractal　dimension　and　the　measured　parameters　such　as　deflection　of　mid-span,　first-order　frequency,　static　stiffness　and　dynamic　stiffness　under　different　fatigue　loadings　and　damage　states.　And　then,　the　matching　relationship　between　fractal　dimension　and　damage　index　was　clarified.　Results　show　that　the　damage　assessment　based　on　fractal　dimension　has　a　good　accuracy　and　robustness,　and　the　refined　damage　assessment　can　be　realized　according　to　the　traditional　physical　parameters　and　the　fractal　dimension　of　cracks.