The anti-galloping combination mode of “double-swing anti-galloping device + cable cleat rotary spacer” is the anti-galloping scheme which is frequently used at present. In order to enhance the anti-galloping capability of Long-span Section over Han River in 1000 kV UHV AC Jingmen-wuhan Transmission line, this text will research the influence of pendulum’s theoretical length on dynamic properties for the double-swing anti-galloping device, which is widely used in the ultra-high voltage line. Theoretical analysis shows that total mass rate of anti-galloping devices, including double-swing anti-galloping device as well as cable cleat rotary spacer, should reach 6.5%, and the pendulum’s theoretical length shoud be 650mm, then the theoretical anti-galloping capability of whole system became optimized.