This　paper　examines　a　beam　with　open　cracks,　which　is　regarded　as　a　non-uniform　beam.　Based　on　the　Bernoulli-Euler　beam　theory,　the　semi-analytical　solution　of　dynamic　characteristics　of　a　simply　supported　beam　and　continuous　beam　with　an　arbitrary　number　of　open　cracks　was　obtained　using　the　modal　perturbation　method.　In　the　modal　subspace　of　the　uniform　beam,　the　variable　coefficient　differential　vibration　equation　of　the　non-uniform　beam　was　converted　to　nonlinear　algebraic　equations.　The　modal　parameters　of　the　cracked　beam　were　solved　using　the　natural　frequency　and　vibration　mode　of　the　uniform　beam.　The　dynamic　test　analysis　of　the　simply　supported　beam　and　two-span　continuous　beam　with　rectangular　open　cracks　indicated　that　the　semi-analytical　solution　was　highly　precise.　Finally,　the　sensitivity　of　the　natural　frequency　to　crack　parameters　was　studied　using　the　semi-analytical　solution　of　dynamic　characteristics　of　the　beam　with　open　cracks.　©　2016,　Editorial　Department　of　JVMD.　All　right　reserved.