A stereo signal encoding method, comprising: determining a target adaptive spreading factor based on a quantized LSF parameter of a primary channel signal in a current frame and an LSF parameter of a secondary channel signal in the current frame; and writing the quantized LSF parameter of the primary channel signal in the current frame and the target adaptive spreading factor into a bitstream, wherein the target adaptive spreading factor is for minimizing a weighted distance between a spectrum-spread LSF parameter of the primary channel signal and the LSF parameter of the secondary channel signal, wherein the determining the target adaptive spreading factor comprises: calculating an adaptive spreading factor based on the quantized LSF parameter of the primary channel signal and the LSF parameter of the secondary channel signal, wherein the quantized LSF parameter of the primary channel signal, the LSF parameter of the secondary channel signal, and the adaptive spreading factor β satisfy the following formula: β = ∑ i = 1 M w i − LSF ̅ S 2 i + LSF S i LSF ̅ S i − LSF S i LSF P i + LSF ̅ S i LSF P i ∑ i = 1 M w i − LSF ̅ S 2 i − LSF P 2 i + 2 LSF ̅ S i LSF P i, wherein LSF S is a vector of the LSF parameter of the secondary channel signal, LSF P is a vector of the quantized LSF parameter of the primary channel signal, LSF S is a mean vector of the L SF parameter of the secondary channel signal, i is a vector index, 1 ≤ i ≤ M, i is an integer, M is a linear prediction order, and w i is an i th weighting coefficient; and quantizing the adaptive spreading factor to obtain the target adaptive spreading factor. determining a target adaptive spreading factor based on a quantized LSF parameter of a primary channel signal in a current frame and an LSF parameter of a secondary channel signal in the current frame; and writing the quantized LSF parameter of the primary channel signal in the current frame and the target adaptive spreading factor into a bitstream, wherein the target adaptive spreading factor is for minimizing a weighted distance between a spectrum-spread LSF parameter of the primary channel signal and the LSF parameter of the secondary channel signal, wherein the determining the target adaptive spreading factor comprises: calculating an adaptive spreading factor based on the quantized LSF parameter of the primary channel signal and the LSF parameter of the secondary channel signal, wherein the quantized LSF parameter of the primary channel signal, the LSF parameter of the secondary channel signal, and the adaptive spreading factor β satisfy the following formula: β = ∑ i = 1 M w i − LSF ̅ S 2 i + LSF S i LSF ̅ S i − LSF S i LSF P i + LSF ̅ S i LSF P i ∑ i = 1 M w i − LSF ̅ S 2 i − LSF P 2 i + 2 LSF ̅ S i LSF P i, wherein LSF S is a vector of the LSF parameter of the secondary channel signal, LSF P is a vector of the quantized LSF parameter of the primary channel signal, LSF S is a mean vector of the L SF parameter of the secondary channel signal, i is a vector index, 1 ≤ i ≤ M, i is an integer, M is a linear prediction order, and w i is an i th weighting coefficient; and quantizing the adaptive spreading factor to obtain the target adaptive spreading factor. calculating an adaptive spreading factor based on the quantized LSF parameter of the primary channel signal and the LSF parameter of the secondary channel signal, wherein the quantized LSF parameter of the primary channel signal, the LSF parameter of the secondary channel signal, and the adaptive spreading factor β satisfy the following formula: β = ∑ i = 1 M w i − LSF ̅ S 2 i + LSF S i LSF ̅ S i − LSF S i LSF P i + LSF ̅ S i LSF P i ∑ i = 1 M w i − LSF ̅ S 2 i − LSF P 2 i + 2 LSF ̅ S i LSF P i, wherein LSF S is a vector of the LSF parameter of the secondary channel signal, LSF P is a vector of the quantized LSF parameter of the primary channel signal, LSF S is a mean vector of the L SF parameter of the secondary channel signal, i is a vector index, 1 ≤ i ≤ M, i is an integer, M is a linear prediction order, and w i is an i th weighting coefficient; and quantizing the adaptive spreading factor to obtain the target adaptive spreading factor.