1. A voice activity detection (VAD) method applied in speech coding, wherein, the method comprises: obtaining sub-band signals and spectrum amplitudes of a current frame; computing values of a energy feature, a spectral centroid feature and a time-domain stability feature of the current frame by using the sub-band signals; computing values of a spectral flatness feature and a tonality feature according to the spectrum amplitudes; computing a signal to noise ratio (SNR) parameter of the current frame with a background energy estimated from a previous frame, the energy feature and an energy of SNR sub-bands of the current frame; computing a tonality signal flag of the current frame with the energy feature, the spectral centroid feature, the time-domain stability feature, the spectral flatness feature and the tonality feature of the current frame; computing a VAD decision result with the tonality signal flag, the signal to noise ratio parameter, the spectral centroid feature, and the energy feature.