Abstract: Emergence of crack causes local flexibility variation of the component.A linear elasticity theory of fracture mechanics is applied to deriving the strain energy released by the crack.According to Castigliano theorem,elements of local flexibility matrix are obtained,which can correct the stiffness matrix of the taper beam.The dynamic behaviour of the taper beam has been found out by means of finite element method.The effects of relative depth of crack,crack location,ratios of length to width and width to taper thickness on natural frequency have been numerically investigated and the relevant experiments have been conducted to testify the calculation results.