The bolts and nuts are widely used in various fields as important joining elements with long history. However, loosening induced by the vibration and external loads is still a big problem. For example, the loosening sometimes causes very serious accident without notice. This paper deals with a special nut named “Super Lock Nut (SLN)” which can prevent loosening effectively. There is a thin walled tube between the upper and lower threads, which can be deformed along the axial direction so that the phase difference of lower and upper threads is produced and SLN is developed. This phase difference induces the contrary forces on the surfaces of the upper and lower threads, which bring out the anti-loosening performance. In this study, the anti-loosening performance is analyzed and realized with the finite element method. Moreover, the anti-loosening performances under various phase difference of lower and upper threads are compared and finally best dimensions for SLN are examined.