For the CNC milling in DMU50 machine tool, the problem to constructing postprocessor based on Edgecam software is researched. In this paper, The general flowchart of post-processing was concerned, the technology of kinematics and the method of construction were proposed, then, the postprocessor of SIEMENS 840D was created by Edgecam, at last, the correctness and validity of the method was certified by simulation and machining in experiments.