Abstract: Aiming at the synchronous axis error of the worm wheel grinding machine, an equivalent compensation method based on the virtual axis was proposed. Firstly, a virtual synchronous axis (SIM1 axis) to the electronic gearbox of the gear grinding machine was added, and an equivalent compensation conversion model was established to convert the error compensation amount of each synchronous axis in the electronic gearbox to the equivalent compensation amount of the virtual axis, and then the final virtual axis equivalent compensation amount was linearly superposed. Secondly, the vertical feed motion locus of grinding wheel was discretized into a series of spline points, and the spline points were selected as error compensation points. The established equivalent compensation conversion model was compiled into the man-machine interface program, and the vertical feed motion locus program of the grinding wheel with the equivalent compensation amount of the virtual axis was automatically generated. Finally, the effectiveness of the equivalent compensation method was verified by the synchronous axis error measurement and the gear machining experiment.