Abstract: A special robot is developed for in-service maintenance of steam generator (SG) in nuclear plant.It is of a two-end 6R serial chain structure.With the help of propulsion device,the robot with 7-axis can enter the limited quarter- sphere chamber through the manhole of the SG,and fix on the tube-sheet with the distensible mechanism at one end.By attaching different tools at the other end,the robot can provide services such as eddy current inspection,ultrasound inspection, plugging,and setting sleeves.In this paper,the new servicing scheme and robotic configuration are presented firstly.Then, by considering obstacle avoidance and two-end operation factors,the robot’s workspace,kinematics solution and compound movement are discussed to confirm the feasibility of the structure scheme.Finally,the robot prototype is tested by field experiment,and the result shows that the robot can meet the requirements of SG maintenance.