Established　the　three　spans　prestressed　continuous　beam　dynamic　equation,　obtained　analytical　expression　of　frequency　equation.　To　solve　the　frequency　equation　for　natural　frequency,　and　compared　with　the　finite　element　numerical　analysis　results,　the　frequency　both　with　analytical　expression　and　with　finite　element　are　in　good　agreement.　The　formula　can　be　obtained　accurately　the　dynamic　parameters　of　three　spans　prestressed　continuous　beam　such　as　frequency.　At　the　same　time,　the　paper　also　studied　the　natural　frequency　sensitivity　analysis　of　three　spans　prestressed　continuous　beam,　and　focuses　on　the　impact　on　the　frequency　with　effective　prestress　and　prestressed　eccentricity.