A solar panel substrate planeness non－contact system, which employs optical triangulation method, and bases on virtual precise measuring datum, is presented. By means of declinate optical triangulation measuring instrument structure which is firstly proposed, the measured area and resolution of this measuring system are greatly increased, and the high accuracy non－contact measurement of the planeness of a large area plane is realized. On the basis of new modeling method of virtual precise measuring datum and measurement error compensation technique, the measuring system can accurately measure the solar panel substrate planeness on a non－precision plate. The actual measurement results show that the measurement accuracy 0.02mm (rms) can be obtained when a solar panel substrate (2581mm×1755mm) planeness is measured by using of this measuring system.