Abstract: Robot CAD system has a particular complex data strucutre, because it involves so1id model, kinematics, dynamics, orbit, environment, and so on. A data base is its necessary tool. This paper discusses the structural character of robot CAD data base, and from actual use, designs a robot CAD data base. With this data base, it designs 3robots in according to actual structure. This paper makes valuable research about the data base for a robot CAD system.