Based on the motion relation between grinding wheel and gear in the process of helical-gear form grinding, the mathematical model of the helical-gear form grinding was established. The theoretical profile of the grinding wheel had been obtained by deducing the contact condition equations between the grinding wheel and the tooth face to be ground. The equidistant curve of the profile of grinding wheel was deduced to meet the need for dressing the grinding wheel by means of diamond wheel. The grinding wheel dressing software and numerical simulation software were developed, which could be used to dress the form grinding wheels with arbitrary helical-gear parameters and test the wheel dressing accuracy. Helical-gear grinding experiments showed that the dressing theory was correct and the dressing software was feasible.