An optimization design method of vibration reduction for ease-off modification based hypoid gears was proposed to improve dynamic performances of automobile drive pinion axle． The modified pinion were represented by a sum of two vector functions determining the tooth of conjugate and the pinion normal ease-off deviations ，which were expressed by both predesigned transmission error function and tooth profile modification curves． Mes-hing stiffness was obtained with tooth contact analysis (TCA) and loaded tooth contact analysis (LTCA)． Based on force analysis of the meshing position，the bending-torsional-axial coupling dynamic lumped mass model for hy-poid gears was established，and the vibration response of the system was obtained by solving the differential equa-tion of motion with numerical method． The best ease-off deviations were determined by a optimizing minimal mean square value of normal vibration． Besides，influences of stiffness curve shape and amplitude caused by modifica-tion on the dynamic performance of the system were explored． A numerical example shows that excessive modifica-tion leads to decrease of meshing stiffness，which are responsible for the increase of normal vibration． In case of a little differences in value of average meshing stiffness for the modified tooth surfaces，the shape is more sensitive to vibration than the amplitude for stiffness curve． After the optimal ease-off modification，the vibration of system is obviously reduced． Besides，the average meshing stiffness decreases a little and main frequency in the stiffness curve is meshing frequency，and there is no frequency doubling component． When the amplitude of load transmis-sion error (ALTE) decreases and the high frequency component in the curve increases，the vibration may not be reduced，and ALTE can basically reflect the variation tendency of vibration with loads．