A novel noncircular gear grinding method by using gear generator with form-grinding has been put forward. Looking on form-grinding as a tooth of shaper, noncircular gear grinding method would be deduced by using noncircular gear tooth generated method in the shaping process. At the same time, the essential motion in the gear grinding process and the structure of gear grinding CNC has been discussed. This method could not only applied to outer noncircular gear with all convex pitch line but also applied to outer noncircular gear with partial concave pitch line and inner noncircular gear. The difficult problem of noncircular gear hard tooth which could not use finishing process was solved, and the noncircular gear application to the place requested high accuracy become possible.