The propagation equation of the elastic wave is more complicated than that of the electromagnetic wave. It is difficult to design medium parameters when controlling the direction of the elastic wave. In order to obtain precise results of elastic wave propagation, the equations were simplified or approximated to achieve the design effect, depending on the actual situation (such as high frequency). Therefore, as impedance matching and lossless dielectric material requirements are difficult to meet, the scattering phenomenon appears in the design of elastic wave propagation in the process of the device. Usually, and the scattering wave is variable frequency signal. It is a way and a tool in the evaluation of elastic wave device design, the size of the scattering phenomenon marks the design effect. The fractional Fourier transform (FRFT), which has good focusing characteristic, is adaptive to analyze frequency variation signal. The frequency change rate provides a quantitative description method of elastic scattering wave propagation control. This reduces the blindness of scattering degree of cognitive, simplifying the dielectric become evaluation of design.