With　an　increasing　number　of　structurally　deficient　bridges,　the　evaluation　and　strengthening　of　the　existing　bridges　have　currently　become　more　concern　for　practical　engineers.　The　bridge　structures　being　of　large　size,　different　structural　forms　and　materials,　the　strengthening　methods　of　the　superstructure　may　be　multiple　and　complex.　Various　strengthening　methods,　their　strengthening　mechanism,　advantages　and　disadvantages　are　summarized　in　the　paper.　Among　these　methods,　the　external　pre-stressing　technology,　changing　the　structural　system　of　original　bridge　and　bonding　carbon　fiber　reinforced　polymer　fabrics　are　recommended　to　strengthen　the　mid-span　and　large-span　bridges.　Several　typical　examples　of　bridge　strengthening　are　demonstrated.