This paper proposes a stable gain scheduling method of linear time invariant controllers for tracking servo system. In order to read and write the data on the optical disc, the pick-up head should be moved to the exact track quickly and follow the track immediately. Two different controllers are used for each moving and track-following. In pull-in period, a transition period from moving to track-following, the head might slip and miss the target track. This brings on another searching process and increases the total time. One way to avoid slipping is to extend the bandwidth of the track-following controller. But, extending the bandwidth could degrade the following performance. More prevalent way is to use one more controller in this pull-in period and switch to the following controller. In general, however, switching or scheduling of stable controllers cannot guarantee the stability. This paper suggests an scheduling method guaranteeing the overall stability not only in a generalized form but also in special form for SISO system. The sufficient condition is derived from the fact that Q factor of a stable controller should be stay in $RH_{infty}$ space. In the experiment, the proposed method shows better performance than the switching method such as shorter time and lower current consumption.