Computer Aided Optical System Design is an engineering practice course for undergraduate students in College of Optical Science and Engineering, Zhejiang University. When the students have just completed Applied Optics course in spring-summer semester, they will take the practice course in a short semester in summer vocation. This is a projectbased practice course, including optical software developing and lens design. The teaching idea is not only to improve the students' engineering skills but also to connect different knowledge they have studied, to build a comprehensive knowledge structure, and to develop the team spirit, organizational capability, leadership and communication skills. This course is designed as an engineering project with a contract between the teacher group and every design group of 3 students. In this paper we describe the course program and how to provide a chance to combine different knowledge into a project. In every student group, developing ray trace software of good reliability is the teamwork, and each student will design a photographic lens independently. The lens with the best optical performance will be selected as the team's result, and be drawn into a system diagram and part drawings. The whole process is both competitive and cooperative, and gives the students the experiences of programmers and lens designers. Most of the students appreciated the practice course and named it as "the most memorable short semester".
