The visible-spectrum gaze tracker gains the advantage of excellent user experience compared with the traditional infra-ray based one. But the head motion compensation becomes extremely difficult due to the lack of stable reference feature points on the eye images. The system performance degrades a lot if the user head is not fixed at the chin rest. This paper presents the compensation mechanism of free head motion for a visible-spectrum gaze tracker. The proposed approach aims at allowing the user to move their heads back and forth. The experimental results show that the accuracy as well as precision can be significantly improved.