This study focus on the stiffness analysis of a three-DOF orientation fine-tuning manipulator for segment assembly robots in shield tunneling machines. In underground space development, shield tunneling machines are widely used in subway tunnels, channel tunnels and other kinds of tunnels. As one of the key sub-devices in a shield tunneling machine, a segment assembly robot is used to automatically form the segment lining. In order to evaluate the operational capacity, an analysis of the inverse kinematics is conducted. The local performance atlas, including stiffness and dexterity, are investigated. The results show that the proposed orientation fine-tuning manipulator has good performances and it can meet the needs.