The principal of how to design a microscope is introduced in this dissertation. There three designs in this thesis: two objectives and an eyepiece, and there specifications are 10X/0.25, 20X/0.45 and 10X/22, respectively. By combining the objectives and the eyepiece, we can make 100X and 200X microscope systems. Code V is used to help us simulate the system, and many details of aberrations and the image quality of the microscope system can be observed in the software. In addition, Strehl ratio of an optical system is a diffraction limited system while the value of a system is higher than 0.8. Therefore, the Strehl ratio in the program is considered to examine the image quality of our microscope system.