Abstract: The design of optical window on a spherical shell in electro-optical systems is introduced. The comparison between conventional design and solid modeling by UG is made by an example of IR window. The former adopts the method of iterative trying, and the latter acquires the correct size and location of the optical window from UG solid modeling and space geometry transform, the latter is more visualized and theoretical sound. According to the optical features and engineering limitations, the installation of the optical window is determined.