Fano resonance is a special effect which can greatly enhance the intensity of the local electric field. For a nanostructure, if the hot spots of different wavelengths are in the same spatial position and the scattering spectrum has a Fano lineshape, the enhancement factor of surface enhanced coherent anti-Stokes Raman scattering can be hugely increased. The Fano resonance effect of a symmetric cross bowtie Au nanostructure was studied by FDTD software, the electric field of the "hot spots" near the middle of the structure was greatly enhanced. In surface enhanced coherent anti-Stokes Raman scattering, this structure can make the enhancement factor to be as high as 1013, enabling the detection of single molecules.