Abstract: Beam splitters for infrared spectrum are used to split the band of 3m to 5m and 8m to 12m in infrared detection devices. A new method of designing and fabricating infrared beam splitters with a conventional coater is introduced. In the course of design, we estimated the highest value of average transmission with the formula of Willey, which was used in the design of the beam splitters. Considering the low precision of the available coater, we attempted to design coating with quarterfilms. For improving transmission from 8m to 12m, a self-prepared low refractive index material was deposited on the coating. The beam splitters for infrared spectrum fabricated met the required technical specifications.