The invention discloses an operating method for replacing 220kV U210B/170 type strain insulator strings in a live mode. Operation is flexible and the problem that the U210B/170 type strain insulator strings of a 220kV transmission line are difficult to replace is effectively solved. An equipotential person enters an electric filed to conduct operation through a horizontal hard ladder, hoisting and installation of tools and devices are convenient, and at the same time, the difficulties of pin taking and socket picking on a wire side of the strain insulator strings which are oversized in disk diameter, ultra-high in self-weight and ultra-long are solved. The angle of a clamping tool bent plate is designed to be effectively matched with the included angle of yoke plates, and stress is balanced. The strength of an insulator cradle satisfies the stability needed by horizontally lifting 17 pieces of U210B/170 insulator strings which are about 200kg, and therefore the insulator strings are kept in a straight line state all the time on the insulator cradle. Movable butt joint design is adopted in a front device of the insulator cradle and a front clamp of the insulator cradle, therefore the length of the insulator cradle and balance stress points of the insulator cradle can be adjusted flexibly and labor intensity of the equipotential person is effectively lowered.