The principle of two-dimensional code is simple. It uses the digital matrix arranged by 1 and 0 to produce the verification function. It is divided into matrix QR code principle and row row QR code principle.

Matrix is encoded by the different distribution of black and white pixels in a rectangular space. In the position of matrix element, if square point, circle point or other points appear, it means "1" in binary, and if there is no point, it means "0" in binary. The arrangement and combination of these points determine the meaning of matrix QR code. Row arrangement is based on one-dimensional code, which is stacked into two or more rows as needed. Because of the increase of the number of lines, it needs to be judged, and its decoding algorithm and software are also very different from one-dimensional codes.

Two dimensional bar code can be divided into stacked two-dimensional bar code and matrix two-dimensional bar code. Stacked two-dimensional bar code is formed by stacking multiple short lines of one-dimensional bar codes. The matrix two-dimensional bar code is composed of a matrix. The binary "1" is represented by the appearance of points at the corresponding element positions of the matrix, and the binary "0" is represented by the appearance of empty points. The meaning of the code is determined by the arrangement and combination of points. Representative stacked two-dimensional barcodes include PDF417, code 49, code 16K, etc. Representative matrix two-dimensional barcodes include code one, Aztec, data matrix, QR code, etc. Two dimensional bar code can be read by laser or CCD reader. （ErWeiMaDeYuanLiJiZuCheng）