Abstract: In response to the problems of artificial low-operation efficiency, high labor intensity, high altitude and high risk in drainage board bolt tightening for high voltage transmission line, a bolt tightening live maintenance robot with double arms and double manipulators was designed in this paper. The key to the successful completion of maintenance work is that double working arms and their ends move from the initial position to the bolt and nut alignment state through the trajectory planning of each joint of the robot. The existed polynomial interpolation of joint trajectory planning depends on trajectory endpoint time, leading to some issues such as the low practicability of the method and the neglect of the constraints of the drive mechanism on the joint state in joint trajectory motion, so an improved polynomial interpolation joint trajectory planning method based on Min-Max time standardization was presented. Based on the method, a solving method of joint motion time ranges which meet the requirements of joint trajectory motion constraints was proposed with articulation motion time as the optimization target. Simulation results show that the joint trajectory of the improved algorithm is only with regard to trajectory endpoint state and motion time, but not to trajectory endpoint time, which further dilutes the influence of trajectory endpoint time on the joint trajectory, and the practicality of the algorithm is also improved. By selecting the optimal trajectory articulation motion time which meets the requirements of whole joint state constraints, the improved algorithm not only avoids the occurrence of overshooting and optimizes the trajectory of each joint, but also improves the efficiency of joint motion. Finally, the engineering practicality of the improved algorithm was verified by field operation test.