A two-dimensional optical identification device for a quick decoding operation in a same gray level and decoding method applied to the same. The two-dimensional optical identification device has at least one two-dimensional optical identification with the same gray level. The two-dimensional optical identification has a first positioning block, a plurality of data blocks, and a second positioning block. The first positioning block has a plurality of first positioning points. The data blocks are placed around the first positioning block. The second positioning block has a plurality of second positioning points and a second direction identification point for providing the direction of the two-dimensional optical identification, and the second positioning block is placed at each boundary of the plurality of data blocks for defining the positions of the plurality of data blocks. The second direction identification point indicates an identification direction of the two-dimensional optical identification.