1. A method for processing noisy speech, comprising: obtaining noise from noisy speech according to a quiet period of the noisy speech, wherein the noisy speech includes speech and the noise, the noisy speech is a frequency-domain signal; obtaining a power spectrum iteration factor of a m th frame of the speech according to a power spectrum of a (m−1) th frame of the speech and a variance of a (m−1) th frame of the speech; wherein m is an integer; determining a moving average power spectrum of the m th frame of the speech according to the power spectrum iteration factor of the m th frame of the speech, a power spectrum of the (m−1) th frame of the speech, and a minimum value of the power spectrum of the speech; determining a signal-to-noise ratio (SNR) of the m th frame of the noisy speech according to the moving average power spectrum of the m th frame of the speech and a power spectrum of the (m−1) th frame of the noise; and obtaining a denoised time-domain speech according to the SNR of the m th frame of the noisy speech i wherein the obtaining the power spectrum iteration factor of the m th frame of the speech according to the power spectrum of the (m−1) th frame of the speech and the variance of the (m−1) th frame of the speech comprises: determining the variance σ s 2 of the (m−1) th frame of the speech, wherein σ s 2 ≈E{|Y(m−1,k)| 2 }−E{|D(m−1,k)| 2 }; wherein Y(m−1,k) denotes the (m−1) th frame of the noisy speech; and E{|Y(m−1,k)| 2 } denotes an expectation of the (m−1) th frame of the noisy speech; D(m−1,k) denotes the (m−1) th frame of the noise; E{|D(m−1,k)| 2 } denotes an expectation of the (m−1) th frame of the noise; determining the power spectrum iteration factor α(m,n) of the m th frame of the speech according to a following formula: α ( m , n ) = { 0 α ( m , n ) opt ≤ 0 α ( m , n ) opt 0 < α ( m , n ) opt < 1 1 α ( m , n ) opt ≥ 1 ; wherein α(m,n) opt denotes an optimum value of α(m,n) under a minimum mean square condition and is determined by _α ( m , n ) opt = ( λ ^ X m - 1  m - 1 - σ s 2 ) 2 λ ^ X m - 1  m - 1 2 - 2 σ s 2 λ ^ X m - 1  m - 1 + 3 σ s 4 , _ wherein m denotes a frame index of the speech; n=0,1,2,3. .. , N−1; N denotes a length of the frame, denotes the power spectrum of the (m−1) th frame of the speech; when m=1,{circumflex over (λ)} X 0|0 =λ min , {circumflex over (λ)} X 0|0 is a preconfigured initial value of the power spectrum of the speech, and λ min denotes a minimum value of the power spectrum of the speech.