Abstarct: Beach cusps are quasi-regularly spaced feature in the swash zone. Many scientists have attempted to explain how beach cusps form and develop. As a result of this work, two contrasting theories for their formation have gained acceptance: the sub harmonic edge wave theory and the self-organization theory. Cusps can change the form of the shoreline in the short period of time but if their embayment's depth and height grows too much, causes erosion of shoreline and if sedimentation in the seaward point horns increases causes sedimentary problems for near facilities and ports. So Knowing about the formation and development of cusps can improve and complete the planning of future engineering projects and management of coastal areas. In this study the formation and development of beach cusps of Roddick beach in the Chabahar city have been discussed. At first, the morphology of the area and then monsoon and ocean storms Introduced and more information of hydrodynamic and classification of coast of Ruddick expressed. In the end, by the Mike 21 software and 18 scenarios, parameters that affecting the change of cusps and the effect of theories that has been said previously, have been investigated. In this study, a new idea expressed that by separating edge wave from wave energy spectrum and compared it to the total run up, the theory of the formation and development of coastal cusps can be determined. The results show that beach Roddick have reflective and intermediate conditions that forming the cusp in there is possible. Increasing wave height and period, increases the size of cusp. For Storm Ocean, there is erosive swash conditions with embayment deepening and so grow thing cusps and the formation of cusps supports edge wave theory. For monsoon storms, there is accretionary swash conditions with horn deposit and so grow thing cusps and the formation of cusps supports self-organization theory.