In order to achieve better speech quality both in high SNR (signaltonoise ratio) and low SNR conditions, this paper proposes a coupled MMSE (minimum mean square error) and WEDM (weighted euclidean distortion measure) spectral amplitude estimations method for speech enhancement. This method employs sigmoid mapping function to map a posteriori SNR into ［0, 1］ range. Thus, according to this mapping function, we develop an adaptive gain function calculation method for spectral restoration. In higher SNR conditions, to prevent speech distortions，the proposed method adopts a larger value of mapping function and makes MMSE spectrum estimation gain function be the gain function for spectral restoration. On the other hand, in lower SNR conditions, to more effectively remove noise from noisy speech, the proposed method uses a smaller value of mapping function and selects the gain function of WEDM spectrum estimation to be the gain function for spectral restoration. Our experiments demonstrate that the proposed method is superior to the reference methods.