In order to improve the meshing performance of gear drive,an Ease- offbased modification method oftooth surface is proposed for spiral bevel gears. By predesigning the contact ratio of gear pair,the symmetric para-bolic function of transmission error and the contact ellipse,a bidirectional modification of the pinion surface is per-formed along the contact path and the contact line,thus obtaining the target tooth surface.Then,a least- square op-timization model is established to identify the machine- tool setting parameters approaching the target surface via theLevenberg- Marquardt method based on a trust- region strategy.The results of numerical examples show that a set ofmachine- tool setting parameters approaching the target surface can be obtained through limited iterations,which en-sures the pre- designed meshing performance and keeps the maximum derivation of tooth surface within 2.0μm; andthat the pre- designed contact ratio,the transmission error amplitude and the contact ellipse all directly affect theiteration times as well as the precision of tooth surface modification.