Abstract: A new coaxial positioning device was proposed to overcome the disadvantage of existing technology, which realized high precision measurement in the shaft hole of optical measuring device. According to three points centering principle and six points axis locating principle, the point contact between six elastic claws and the mechanical axis of shaft hole is a kind of rigid contact and it can bear higher load, and the optical axis of measuring device and mechanical axis of shaft hole can achieve precise coincidence, which makes high precision positioning and good coaxiality possible. It was proved that the positioning device could enable optical measuring device to position accurately in shaft hole with the precision of 10 in theory and in practice.