The gear modification is an important technique to improve gear transmission performance. A new topological modification method with circular tooth profilein gear cutter and tooth drum-shaped is put forward. Based on the gear meshing theory and the tooth contact analysis（TCA） technology,the modification parameters for helical gear are designed,and error sensitivity is studied,that is,the effects of helix angle and pressure angle errors on the transmission error and contact trace. The study shows thats gear with the proposed topological modification is insensitive to the helix angle and pressure angle errors,and it has good performance without edge contact. The result provides a theoretical foundation for the modification of helical gear.