Sealing life is a key factor to influences the tool life,and an important index for judging the power tool performance.The structure and principle of lip seal was introduced.A sealing system included dynamic and static sealing used in the power tool armature shaft was introduced.The sealing lip strain and stress under working conditions was analyzed by using ABAQUS/CAE,and the sealing life was tested by experiment.The simulated and test results prove the effectiveness of this sealing system.