1. A method for vector quantization comprising: performing, by a hardware processor, a quantization process on a vector to be quantized by use of N basic codebook vectors and adjustment vectors of the N basic codebook vectors; generating a basic codebook vector and an adjustment vector used for quantizing the vectors to be quantized; combining the basic codebook vector and the adjustment vector to different basic sub-vectors as a joint codebook vector; and selecting a joint codebook vector for quantization among possible joint codebook vectors according to the deviation between the joint codebook vector and the vector to be quantized; wherein: N is a positive integer larger than or equal to 1; each basic codebook vector and each adjustment vector have same dimensions; and selecting the joint codebook vector for quantization among possible joint codebook vectors according to the deviation between the joint codebook vector and the vector to be quantized comprises: calculating a residual vector between the vector to be quantized and the current basic codebook vector obtained from the basic codebook unit; wherein the residual vector has one or more residual sub-vectors, and the way of dividing into residual sub-vectors is the same as the way of dividing into basic sub-vectors; for a basic sub-vector corresponding to an adjustment vector collection, selecting a best adjustment vector of the current basic sub-vector according to the deviation between the adjustment vector in the adjustment vector collection provided by the adjustment vector unit and the corresponding residual sub-vector; accumulating a deviation of best adjustment vectors, and the deviation between the basic sub-vector not corresponding to the adjustment vector collection and the vector to be quantized, and using such a deviation as the deviation of the best joint codebook vector corresponding to the current basic codebook vector; and comparing the deviation of the best joint codebook vector corresponding to each basic codebook vector, and selecting a joint codebook vector for quantization.