Abstract: Due to the stego image double compressed before embedding in some steganographic techniques,double compression could be one of the features of steganography.After JPEG double compressed,the DCT statistic of JPEG image will be changed,which is the focus of this paper.The distributions of DCT coefficients are changed with the double compression quantization tables q_1,q_2.The difference of the distributions is analyzed.The different detection methods are proposed based on different q_1,q_2 which are effectively proved by the experiments.