To help solve the problems existed in current RP systems using STL data model, which are low precision, hard to
distribute efficiently among various CAX systems, and to establish some fundament for RP system based on STEP-NIC,
this article studied the gathering method of 3-d geometric model feature of STEP-NC. Based on the in-depth analysis of
AP203 neutral file's structure and its description language EXPRESS, a data gathering module for AP203 neutral
exchange file was made in the form of a dynamic link library, achieved the goal of correctly acquiring the STEP-NC 3-d
CAD model's geometric and topologic feature information. This provides the fundament for achieving slicing of
STEP-NC and developing corresponding RP system.