An optical recognition pattern for length measurement is mounted on an optical contact surface and includes a plurality of optical recognition units, each of which corresponds to a length value. The sequence of the optical recognition units on the optical contact surface is consistent with that of the corresponding length values in such a way that the optical recognition pattern imitating the conventional measuring ruler can be constituted. Besides, the optical recognition pattern can further work with an optical recognition device to constitute a length measurement system that the optical recognition is applied to.