1. A voice activity detection method, comprising: obtaining a combined voice activity detection, VAD, judgment result according to the number of continuous active frames, an average total signal to noise ratio, SNR, of all sub-bands, a tonal signal flag and at least two existing VAD judgment results; wherein, the method further comprises: obtaining a sub-band signal of a current frame; calculating frame energy parameters according to the sub-band signal; obtaining background noise energy estimated from a previous frame; calculating the average total SNR of all sub-bands according to the background noise energy estimated from the previous frame and frame energy parameters of a current frame; wherein, said obtaining the background noise energy estimated from the previous frame comprises: obtaining a sub-band signal and a spectrum amplitude of the previous frame; calculating frame energy parameters, spectral centroid features and time-domain stability features of the previous frame according to the sub-band signal of the previous frame; calculating spectral flatness features and tonality features of the previous frame according to the spectrum amplitude of the previous frame; calculating a background noise flag of the previous frame according to the frame energy parameters, the spectral centroid features, the time-domain stability features, the spectral flatness features and the tonality features of the previous frame; calculating a tonal signal flag of the previous frame according to the tonality features, the spectral centroid features, the time-domain stability features and the spectral flatness parameter of the previous frame; obtaining the energy of background noise over all sub-bands of the previous frame according to the background noise flag, the frame energy parameters and the tonal signal flag of the previous frame and the energy of background noise over all sub-bands of a frame before previous frame.