According to the theory of Fabry-Perot (F-P) interference, the measurement of no plated membrane light filter is implemented by choosing flat glass (SiO2) as interferometric cavity of the measurement system, and adopting the method for measuring the extremum between two nearby interfered lights. It is the most important part of the new Ultra-narrow Bandwidth filter. Based on solid-cavity thickness of supper narrow band optical comb filters, the precision of height measurement comes true. Experimental results indicate that the accuracy of the optical measurement system with simple configuration and low-cost reaches subnanometer level, as well as strong anti-jamming and stabilization. The system can be adapted to measure transparent medium such as plat-glass, filters, optical coating as well as no plated membrane filters.