Abstract: Two copies of stego-image are needed in the active steganalysis proposed by Chandramouli,as an improvement,a method of active steganalysis is proposed in which only one copy of stego-image is needed and the practicability is enhanced.An estimate of a cover image by wavelet-domain hidden Markov tree(HMT) is obtained;and the estimate is regarded as another stego-image which is different in the embed ratio.Then cover image and the secret message are separated by using the independent component analysis(ICA).Simulation experiments validate the advantage of HMT model,and give the results of blind separation.