In order to study the influence of pitting defect on the contact stress of face gear, a face gear of helicopter transmission system was taken as the research object, the defect shape was assumed to be spherical and the solid model was built by UG and Catia software. Using the finite element loading tooth contact analysis method（LTCA）, the contact stress distribution and variations of maximum contact stress value and its position are obtained when the defect is in different position on the tooth surface. The results show that the introduction of pitting defect can increase the maximum contact stress of tooth surface by 21%. When the defect is close to the contact trace line and tooth tip, the maximum contact stress is greater than that of other positions. The maximum contact stress occurs near the middle or upper part of the defect, its position is on the right of the defect while the defect is outside the contact trace line, and it is the opposite when the defect is inside the contact trace line. The maximum contact stress near the defect increases with the increase of defect radius gradually. The influence of defect depth on contact stress is small.