The design of tea production line was considered in a 3-D level, and it was transformed into an assembly modeling problem. At first, a position irrelevant plane layout method was introduced which made the frequent adjustment of devices’ positions unnecessary, thus the workload of designers were relieved dramatically. Then, with the orientation coding of devices and their connection relations, absolute and relative orientation of devices were determined. Finally, datum constraints were exerted to devices which realize the assemblying or positioning of devices automatically, rather than manual. According to this idea, by secondary development of SolidWorks, a program called TPLLayout was written by VB 6.0. The example showed that the system was user-friendly, and easy to operate, which improved the design efficiency dramatically, and the cost was reduced as well.