Abstract: The invention relates to a method for coding a two dimensional (2D) optical identification (OID) with the same gray level and a printing product thereof. The printing product includes a 2D-OID, which includes a positioning block and a plurality of data coding blocks. The positioning block has a plurality of specific patterns arranged as an N×M matrix, wherein the specific patterns along a first edge thereof and the specific patterns along a second edge thereof are filled. The data coding blocks are disposed around the positioning block and include the specific patterns arranged as the N×M matrix, wherein the specific pattern in a center of the data coding blocks is filled. A specific number of the remaining specific patterns in each data coding block are filled to serve as a code for representation of data.