An approach of localizing the contact zone of the double-envelope hourglass worm gearing has been proposed to reduce the sensitivity to the errors and the load. The influence of the errors on the contact zone is systematically investigated. The contact deformation, the shift of contact zone and load share among the meshing tooth-pairs has been analyzed using 3D contact FEM. After synthetically considering the influence of the errors and the load, the worm surface is modified into the crowning in height direction in comparison with the hob. The results from the loaded contact analysis demonstrate that this modification drive can absorb the influence of the errors and the load on meshing performance