Abstract: The simulation of gear meshing is performed by TCT programs in the light of the assumption that gear tooth surfaces are in contact at every instant.But the edge contact may occur due to misalignment,deflection of teeth and unsuitable machine-tool settings.So the vibration and noise of gear drives are inevitable.A new simulation method of the edge contact for hypoid gear and spiral bevel gears is provided.The contact patterns and transmission errors for the aligned and misaligned gear drives are obtained in an example of spiral bevel gears.Although the proposed method deals with the hypoid gear and spiral bevel gears,the basic idea is suitable for spur and helical gears.