Abstract: Abstract：In strong reverberant environment, blind separation of speech signals under convolutive mixture is a difficult problem, since the conventional algorithms will degrade quickly due to long reverberant time., which is longer than the nonstationary time of speech. A new method is proposed to deal with this case, where two short time Fourier transforms (STFT) are used to transform time signals into frequency domain, so the convolutive mixture with long reverberant time in time domain can be expressed as the instantaneous mixture in the modulation spectrogram, and some algorithms for instantaneous mixture can be applied easily. In this paper, the Independent Vector Analysis (IVA) algorithm is proposed to avoid permutation ambiguity efficiently in the modulation spectrogram. The computer simulations confirm that the proposed algorithm outperforms conventional frequency domain BSS algorithms in strong reverberant environment.