A touch device warning method and a touch device warning system are provided. The touch device warning method provides multiple judgment mechanisms. The multiple judgment mechanisms include the mechanism of judging whether a touch device is triggered by a touch pen, the mechanism of judging whether the touch device is moved and the mechanism of judging whether an untouched time period of the touch pen and the touch device exceeds a predetermined time. Once the conditions of the judgment mechanisms are satisfied, the touch device warning method warns the user of taking back the touch pen. Consequently, the possibility of losing the touch pen is reduced, and the occurrence of the erroneous judgment is avoided.