This disclosure provides an encoding method, a decoding method, an encoding apparatus, and a decoding apparatus for a stereo signal. The encoding method includes: performing interpolation processing based on the inter-channel time difference in the current frame and an inter-channel time difference in a previous frame of the current frame; performing time-domain downmixing processing on the stereo signal after the delay alignment in the current frame, to obtain a primary-channel signal and a secondary-channel signal in the current frame; and quantizing the inter-channel time difference after the interpolation processing in the current frame, the primary channel signal and the secondary channel signal.