A stereo encoding method, comprising: performing time domain preprocessing on a left channel time domain signal and a right channel time domain signal that are of a current frame of a stereo audio signal, to obtain a preprocessed left channel time domain signal and a preprocessed right channel time domain signal that are of the current frame; performing delay alignment processing on the preprocessed left channel time domain signal and the preprocessed right channel time domain signal that are of the current frame, to obtain the left channel time domain signal obtained after delay alignment and the right channel time domain signal obtained after delay alignment that are of the current frame; determining a channel combination solution of the current frame based on the left channel time domain signal obtained after delay alignment and the right channel time domain signal obtained after delay alignment that are of the current frame; obtaining a quantized channel combination ratio factor of the current frame and an encoding index of the quantized channel combination ratio factor based on the determined channel combination solution of the current frame, and the left channel time domain signal obtained after delay alignment and the right channel time domain signal obtained after delay alignment that are of the current frame; determining an encoding mode of the current frame based on the determined channel combination solution of the current frame; downmixing, based on the encoding mode of the current frame and the quantized channel combination ratio factor of the current frame, the left channel time domain signal obtained after delay alignment and the right channel time domain signal obtained after delay alignment that are of the current frame, to obtain a primary channel signal and a secondary channel signal of the current frame; and encoding the primary channel signal and the secondary channel signal of the current frame. performing time domain preprocessing on a left channel time domain signal and a right channel time domain signal that are of a current frame of a stereo audio signal, to obtain a preprocessed left channel time domain signal and a preprocessed right channel time domain signal that are of the current frame; performing delay alignment processing on the preprocessed left channel time domain signal and the preprocessed right channel time domain signal that are of the current frame, to obtain the left channel time domain signal obtained after delay alignment and the right channel time domain signal obtained after delay alignment that are of the current frame; determining a channel combination solution of the current frame based on the left channel time domain signal obtained after delay alignment and the right channel time domain signal obtained after delay alignment that are of the current frame; obtaining a quantized channel combination ratio factor of the current frame and an encoding index of the quantized channel combination ratio factor based on the determined channel combination solution of the current frame, and the left channel time domain signal obtained after delay alignment and the right channel time domain signal obtained after delay alignment that are of the current frame; determining an encoding mode of the current frame based on the determined channel combination solution of the current frame; downmixing, based on the encoding mode of the current frame and the quantized channel combination ratio factor of the current frame, the left channel time domain signal obtained after delay alignment and the right channel time domain signal obtained after delay alignment that are of the current frame, to obtain a primary channel signal and a secondary channel signal of the current frame; and encoding the primary channel signal and the secondary channel signal of the current frame.