The invention provides a pre-positioned boss positioning device, and can solve the problems that during pre-positioning on a turbine blade with a damping boss, detection correction is carried out after positioning of a blade top center hole, the position of a blade root relative to a blade body molded surface cannot be controlled effectively, and the processing precision of the blade root is affected. The pre-positioned boss positioning device comprises a bottom plate, a side surface positioning seat and a working surface positioning plate, wherein a side surface positioning block, an adjusting support and an angled pressing seat are arranged on the side surface positioning seat; a positioning surface of the side surface positioning block is attached to the side surface of a back arc bossof a damping boss; the adjusting support is arranged vertically, and a supporting end of the adjusting support is abutted against to the inside of a transition groove between an inner arc boss workingsurface of the damping boss and the blade body molded surface; a pressing screw is mounted on the angled pressing seat; the head of the pressing screw is abutted against a transition region between the bottom of an inner arc boss of the damping boss and the blade body molded surface; a positioning plate of the working surface is horizontally attached to the upper end surface of the side surface positioning seat; and the positioning surface of the working surface of the boss is attached to the working surface of the back arc boss of the damping boss.