By thoroughly analyzing the characteristics of 3-axis milling of circular/annular region, planar variable radius helical interpolation (PVRHI) was proposed. Based on group technology, using polar function of CNC machine, a parametric program oriented circular/annular region features was provided. CNC machining on 3-axis milling machine of circular/annular/planar thread features could be realized by proper assigning for variables. The VERICUT simulation results and the experiment result on 3-axis CNC machine show that the PVRHI is highly effect and correct.