Scour has caused huge economic loss and casualties in human history by making bridges failed. The influence of scour on security of bridges may be assessed by analysing the variance of dynamic properties of bridges. This article analyzes the influence of scour on dynamic properties of bridges from two aspects of scour depth and area loss. Based on reviewing existing analytical methods of model, a finite element model is used to analyze the relationship between scour and dynamic properties of an existing failed bridge called MS HWY 33bridge.