Abstract: In order to balance the energy mismatch between the training data and test data in the speech enhancement method based on Mel-Frequency Spectral domain Hidden Markov Model (Mel-Frequency Spectral domain Hidden Markov Model, MFS-HMM),an energy adjustment method is proposed for MFS-HMM based speech enhancement. In this method, the online estimation of the log-energy adjustment factor for clean speech and noise is obtained by the iterative expectation maximization (EM) method, and the parameters of HMMs of clean speech and noise are modified online, respectively. This makes the energy of training data match to the test data better and the effect of energy mismatch on the enhanced speech is reduced efficiently. Experimental results of subjective and objective qualities show that, in comparison with the reference methods, the proposed method can get better performance.