Large Optical Antarctic Telescope, LOAT hereafter, is a new research hotspot nowadays. For example, a 2.5m KDUST, e.g. Kunlun Dark UniverSe Telescope is on anvil. It's difficult for main axis of large telescope tracking system to track the target precisely with ultra-low speed because of nonlinear disturbances due to unique ultra-low temperature. This paper presents these nonlinear disturbances.