The invention provides a tension insulator replacing method of a live-line work robot. The live-line work robot comprises a mechanical arm arranged on a robot platform. The mechanical arm comprises a first mechanical arm, a second mechanical arm and an auxiliary mechanical arm. The first mechanical arm, the second mechanical arm and the auxiliary mechanical arm respond to finishing of replacing of the tension insulator by the control data, wherein the control data is an angle expected value of joint movement of each mechanical arm. During the shaking operation, the data processing and the control system carries out resolving according to each joint angle change data of a main manipulator, so the angle expected values are acquired. During autonomous working, the data processing and control system plans out a space path of each mechanical arm by using the Cartesian space route planning method, and the resolves the angle expected value of the joint movement of each mechanical arm. According to the invention, the tension insulator can be changed through the mechanical arm of the live-line work with no need to cut off the electricity and carry load.