Abstract: A solar panel substrate planeness non-contact system is presented, which employs optical triangulation method and bases on virtual precise benchmark. 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 a new modeling method of virtual precise measuring benchmark and measurement error compensation technique, the measuring system can accurately measure the solar panel substrate planeness on a non-precision plate. In addition, in order to lay a theoretic foundation for optimization design of the laser spot, the relationship between measuring laser spot positioning accuracy and the shape, size and energy distribution of spot image, is analyzed deeply. 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.