A stereo signal encoding method includes obtaining a residual signal encoding parameter of a current frame of a stereo signal based on downmixed signal energy and residual signal energy of each of M sub-bands of the current frame, where the residual signal encoding parameter indicates whether to encode residual signals of the M sub-bands, determining whether to encode the residual signals based on the residual signal encoding parameter, and encoding the residual signals when it is determined that the residual signals need to be encoded.