Recommendatory parameters of grinding wheel radius （ r a）and grinding wheel axial inclined angle （ β ） have been givenwhen dual conical surfaces generated double enveloping worm gearing has been generated in different series of gear ratio and center distance. The methods to choose modification parameters of type Ⅱ have been given. The mismatched meshing analysis of dual conical surfaces generated double enveloping worm gearing has been done. The results show that worm gearing of type Ⅱ and standard type are obviously sensitive to errors. A mismatched modification which synthetically revise the r a、 β and the profile angle （ α 2） of grinding wheel

all of which are used to manufacture worm and hobbing cutter

has been proposed. The tooth contact analysis shows that good modification effect is achieved when the method of tooth mismatched modification is used.