Exposed porcelain insulator strings need regular cleaning to prevent power failures caused by flashovers from occurring. Live-line cleaning of insulators using robot technology is an alternative and novel approach to removing the contaminants on the surfaces of the insulator. This paper presents a live-line insulator cleaning robot for suspension insulator strings in 500kV power transmission lines. After analyzing the cleaning task, we introduce the mechanical system composed of the inchworm-based locomotion mechanism and the cleaning mechanism. The details of the mechanical design are given. The control system composed of the local controller and the ground control station is implemented. The hardware of control system is based on the Digital Signal Controller and the software is developed based on the Real Time Operating System. The motion planning algorithm for the cleaning task is presented. The motion planning model is established in Matlab and simulation results prove the correctness of the motion planning algorithm. Preliminary experiments are carried out, and the results demonstrate the validity and the feasibility of the robot.