Reasonable design of multilayer film system for quartz optical substrate is the key method to improvethe transmittance of optical devices. We designed two different film structures and analyzed the designprinciples of these two systems via admittance loci method.The optical thin film design software Filmstar is usedto obtain the optimal solution of the two film systems respectively ,so that the average transmittance of the filmsystem in the visible region is as close as possible to 100%.