Contact characteristics of hypoid gear are extremely sensitive to installation error, and improper design parameters of tooth surface can cause vibration and noise. A gear tooth optimization design method for reducing installation error sensitivity was proposed to solve these problems. Firstly, a tooth surface contact characteristic evaluation model considering the installation error is proposed, including the change of contact area, the offset of the center point coordinates of the contact trace, and the change of the amplitude of the transition point of the transmission error curve. Then, a NURBS surface fitting method with degradable parameterization is proposed to carry out TCA contact analysis, and the mapping relationships among mounting error, tooth preset control parameters, tooth machining parameters, and contact feature parameters are established; Further, the influence law of mounting error on tooth face contact characteristics is revealed, the comprehensive sensitivity model of single contact characteristic parameter to mounting error is constructed, and based on the conclusion of sensitivity analysis, the sensitivity evaluation method of overall contact characteristics to mounting error is proposed. Finally, with the lowest sensitivity as the optimization goal, the optimization design of tooth preset parameters was carried out by genetic algorithm. Taking two groups of typical working conditions as an example, the comparative analysis of the meshing characteristics before and after optimization reveals that the sensitivity of the optimized tooth flank contact area area, the contact trace center point coordinates and the amount of change in the transmission error to the mounting error are all reduced. The tooth surface optimization design method proposed in the paper can effectively address the issue that the tooth surface contact characteristics are extremely sensitive to installation errors, and reduce the vibration and noise during transmission.