Signal and it's Fourier transform can reflect the info of time domain and frequence domain independently. As a usually math tool, Fourier transform is using in math, physical and engineering field widely. A new tool for signal analysis,which is named Fractional Fourier transform(FRFT), is introduced. It is interpreted in view of the classic Fourier transform. It is important to study the numerical algorithms of FRFT, because usually the FRFT can not be given to a analytical expression. A numerical algorithms of FRFT is given. It is possible to separate the distortion from the simple Gaussian signal on which a chirp distortion has been superimposed by using fractional transform.