The　dynamic-based　structural　evaluation　and　strengthening　of　Dongshan　arch　bridge　were　involved　in　this　paper.　Firstly,　the　disease　and　strengthening　design　measures　were　briefly　introduced.　The　field　ambient　vibration　testing　on　the　bridge　before　and　after　strengthening　was　then　conducted.　After　that,　the　3-D　finite　element　model　of　the　bridge　before　and　after　strengthening　were　established　and　calibrated　according　to　the　field　vibration　testing.　Based　on　the　calibrated　model,　the　static　behavior　of　the　bridge　was　finally　predicted.　The　load-carrying　capability　of　the　bridge　after　strengthening　satisfies　requirements　of　the　load　level　of　truck-load　20　and　trail-road　100　in　Chinese　bridge　code.