Abstract: Sub-span oscillation is a phenomenon of multi-bundled conductors vibration within the sub-span caused by the wake effect of wind, which has become a major disaster to the safe and stable operation of transmission lines. In order to reduce transmission line sub-span oscillation, a new type of damping spacer is presented and designed. First, the vibration absorption and vibration reduction mechanism of the new damping spacer is analyzed by establishing the vibration balance equation, and the influences of changes in the damping ratio, natural frequency ratio and mass ratio on its vibration damping performance are explored in detail. At the same time, a finite element model of the new damping spacer and split conductor system is established by using numerical methods, and the vibration reduction effect of the new damping spacer on the sub-span oscillation is studied. By comparing the vibration reduction effect with that of the ordinary spacer, it is found that the horizontal and vertical displacements of the middle point of the spacer rod are greatly reduced by installing the new type damping spacer; the new type damping spacer has a significant vibration reduction effect on the sub-span oscillation of the transmission line. Finally, the structural parameters and installation positions of the new damping spacer are optimized and designed, and the values of the weight, spring stiffness and damping coefficient of the new type damping spacer, as well as the unequal spacing installation plan of the damping spacer, are given.