The low precision and low efficiency of the machining are the main factors that restrict the development of the hourglass worm.Aiming at precision grinding planar enveloping hourglass worm and the conical surface enveloping hourglass worm,using virtual center distance principle,a seven axis four linkage CNC hourglass worm grinding machine was developed.The left and the right tooth surface grinding of the workpiece was completed automatically with a single chucking.The operator did not need manual programming,the processing procedure could automatically generated once input the workpiece parameters in the grinding software.Cuttingexperiments of planar enveloping hourglass worm was processed on the CNC worm grinding machine.The results show that the modification is feasible and the precision is up to expectations.