According　to　the　structure　characteristics　of　the　non-uniform　beam　bridge,　a　practical　model　for　calculating　the　vibration　equation　of　the　non-uniform　beam　bridge　is　given　and　the　application　scope　of　the　model　includes　not　only　the　beam　bridge　structure　but　also　the　non-uniform　beam　with　added　masses　and　elastic　supports.　Based　on　the　Bernoulli-Euler　beam　theory,　extending　the　application　of　the　modal　perturbation　method　and　establishment　of　a　semi-analytical　method　for　solving　the　vibration　equation　of　the　non-uniform　beam　with　added　masses　and　elastic　supports　based　is　able　to　be　made.　In　the　modal　subspace　of　the　uniform　beam　with　the　elastic　supports,　the　variable　coefficient　differential　equation　that　describes　the　dynamic　behavior　of　the　non-uniform　beam　is　converted　to　nonlinear　algebraic　equations.　Extending　the　application　of　the　modal　perturbation　method　is　suitable　for　solving　the　vibration　equation　of　the　simply　supported　and　continuous　non-uniform　beam　with　its　arbitrary　added　masses　and　elastic　supports.　The　examples,　that　are　analyzed,　demonstrate　the　high　precision　and　fast　convergence　speed　of　the　method.　Further　study　of　the　timesaving　method　for　the　dynamic　characteristics　of　symmetrical　beam　and　the　symmetry　of　mode　shape　should　be　developed.　Eventually,　the　effects　of　elastic　supports　and　added　masses　on　dynamic　characteristics　of　the　three-span　non-uniform　beam　bridge　are　reported.