This paper deals with the development of a computer aided fixture planning system that automatically selects set-ups, set-up sequence and fixture design for prismatic parts. This study presents the hierarchical data structure for feature-based part model and the preprocessing procedure for the proposed system. The preprocessing procedure generates tools such as DDR(Degree of Dimensional Relationship), AMV(Admissible Misalignment Value) and the datum reference frame of each feature according to the proposed decision table. The proposed system is called AFIX(Automated FIXture planning system) which is implemented by using C language on the workstation. A case study for a cavity plate is presented to show the performance of the AFM.