With the increase of rotating speed, the rotor unbalance of the modern rotating machinery becomes more sensitive. The on-line active balance is an ideal balancing mode for precision machines. Electromagnetic balancer is a non-contact new-structure balancing device in the on-line balancing field, as it can reliably work in high-speed condition and keep the position balanceable after turning down. Balance ability is an important indicator evaluating the performance of a balancer. This paper studies a new electromagnetic balancer carrying permanent magnet for the motorized spindle. Because the counterweight disk is the primary moving element of the balancer, its balance compensation value and distribution are mainly discussed in this paper. Based on the existing disk structure, the balance ability of disks with different structure is researched. The two counterweight disks with the same compensation value and distribution angle, the two disks have the same compensation value and different distribution angles, the two disks have different compensation values and the same distribution angle are analysed. The calculation results demonstrate that the first scheme is proven better in the balance ability and can be easily developed.