In order to improve the surface quality of fused deposition modeling (FDM) parts, a post-processing method of NC machining for FDM products was presented. The effects of process parameters such as printing speed, extrusion speed and thickness of the layer on the forming error and surface roughness of molded parts were studied. The effects of NC machining on machining error and surface roughness were studied. The results show that the surface roughness of FDM parts is large, the maximum value reaching 24.434 μm. The forming error of FDM parts can be effectively reduced by reasonably setting the printing speed, extrusion speed and layered thickness. The surface roughness of FDM parts can be effectively reduced by NC machining，the value reaching 1.979~2.446 μm.