A reverse twist defect deteriorates a picture quality of an In-Plane Switching (IPS) mode display. We have proposed a simple method to evaluate the reverse twist stability using a sine curve director profile approximation. The calculated stability has been corresponded to the observed phenomena. Using this method, the stability dependence on the device parameters can be investigated with facility and the deterioration due to the reverse twist defect can be predicted. In the present study, the stability dependence on the rubbing angle, the driving voltage and the cell gap has been examined. The preferable cell gap condition has been suggested to prevent the reverse twist defect.