The similarity of the element of matrix after DCT is studied by theory with changing of brightness or contrast, and with transformation of mirroring or transposing. On the other hand, by making full use of the characteristic, an adaptive matching approach based on DCT is proposed. With respect to matching criterion and robustness of noise interference, attention is mainly given to a majority of energy, so it can meet the demand when only matching a few elements of matrix on the upper-left corner after transform. Experimental result proves that the method based on DCT is perfect.