National working standard of two-dimensional line scale based on laser two-coordinate standard device was set up to solve the problem of the calibration and traceability of 2-D line scale optical standard and high precision photomask. The operating principle and system composition of the working standard device were introduced. The characteristics were test in special experiments. A high precision differential laser interferometer system was used for a length standard, a high magnification optical microvision system was used for precision optical positioning feedback. In order to improve the measuring accuracy, several high precision sensors were installed to measure environmental parameters for compensating the laser wavelength in atmosphere according to the empirical Edlén equation. High resolution CCD modeling and calibrating based on two-dimensional nanoscale positioning movable platform and laser interferometer were adopted to improve the pointing accuracy. Two-dimensional line scale working standard could be used to measure line spacing, point spacing, and coordinates of 2-D optical standard or photomask, with measurement range 300mm × 300mm, measurement uncertainty U=(0.1~0.3)μm, k=2. Some experiments were carried out to identify the characteristics of length measurement error, probing error, measurement repeatability and measurement reproducibility of the working standard, and measurement uncertainty was validated by the measurement experiments.