the grazing periodic motion is likely to change qualitatively for a tiny variation in system parameters; that is, grazing bifurcation will take place. as a result, impact periodic motion or nonimpact periodic motion will occur. obviously, the method for impact periodic motion cannot be applied directly to grazing periodic motion. by extending the discontinuity mapping introduced in [4, 9], we derive a new discontinuity mapping near the double grazing orbit. and then we will analyze the grazing bifurcation with the help of the discontinuity mapping obtained.