This paper describes the forming of fine gear housing using RP system. In order to apply 3D model formed through CAD software to RP system, it is necessary of transforming 3D model into STL file format. Besides, when the same shape is formed repetitively, we must solve the program that the shape accuracy of prototype is irregular. Therefore, we will make an experiment on influence of 3D model, file transformation and prototype on facetres, AutoCAD system value. On the basis of experimental result, we will develop an automatic file transformation program for RP. In the final process, we will manufacture on a better prototype according to the experiment result of fine gear housing.