Abstract: IR/MMW frequency divider is one of the key devices of IR/MMW composite-detected system. The influence of dielectric material characteristic parameters on millimeter-wave transmission, reflection and absorption properties were analyzed and calculated, which was based on theory of electromagnetic interference. The dielectric material thickness design guidelines in 35 GHz was put forward, the influence of SiO2 material different physical thickness and physical thickness deviation on the millimeter-wave transmission properties was analyzed. The results indicate that with the increase of physical thickness, the physical thickness deviation has more influence on millimeter-wave transmission, reflection and absorption properties, the accuracy requirements for physical thickness deviation becomes higher. This article have a certain reference value about the design of IR/MMW frequency divider.