Based　on　forced-vibration　testing　and　finite　element　dynamic　analysis,　the　basic　dynamic　characteristics　of　a　prestressed　concrete　beam　are　obtained.　Furthermore,　the　changes　of　its　dynamic　characteristics　with　different　pres-tressing,　different　prestressing　cable　shapes　and　different　positions　of　prestressing　cables　are　also　examined.　It　is　demonstrated　that　the　existence　or　not　of　prestressing,　and　the　locations　of　prestressing　cables　have　certain　effects　on　the　natural　frequencies　of　the　beam,　but　effects　of　prestressing　values　and　shapes　of　prestressing　cables　on　its　natural　frequencies　can　be　neglected.　This　analysis　is　helpful　to　structural　health　monitoring　and　damage　detections.