Abstract: Fourier transform is usually used in the domain of frequency-wave number transformation in ground penetrating radar. But the interpolation algorithm needs all the data in the domain of frequency migration. So discrete cosine transform (DCT) is presented to replace Fourier transform to do migration. According to the character of the concentration of energy of DCT, the interpolition processing is applied only to the data related with main components on DCT in the domain of frequency. Test result shows that DCT can be a good substitute to Fourier transform and suggested optimization algorithm has less computation and no plural parasitic data.