The invention discloses a prior signal-to-noise ratio estimating method based on an MMSE error criterion and used for voice enhancement, and belongs to the technical field of voice signal processing. Aimed at the prior signal-to-noise ratio estimating problem in the voice enhancement technology, the method comprises the steps of: firstly carrying out preliminary estimation on a prior signal-to-noise ratio of noised voices based on the MMSE error criterion, carrying out Wiener filtering calculation on an obtained prior signal-to-noise ratio estimated value to obtain a first system gain factor, carrying out calculation on the first system gain factor an amplitude spectrum value of the noised voices to obtain a voice power spectrum estimated value, then utilizing the obtained voice power spectrum estimated value and a power spectrum estimated value of noise to carry out estimation once again, and obtaining a final prior signal-to-noise ratio estimated value. The prior signal-to-noise ratio estimated value is substituted into a subsequent voice enhancing step for processing, and de-noised estimated voice clearing signals are obtained. The prior signal-to-noise ratio estimating method based on the MMSE error criterion can effectively inhibit background noise components in estimated cleared voices, and excessive damages to the cleared voice components are avoided, so that the hearing quality of the estimated cleared voices is improved, and the performance of a voice enhancement algorithm is improved.