Friction stir welding (FSW) is a solid-state joining process utilizing a rotating tool, which consists of a pin and tool shoulder that apply severe plastic deformation and frictional heating into the base material. The softened material is extruded underneath and around the tool as the tool travels along the welding line and subsequently meets to form a strong metallurgical joint. Quality and welding rate is highly dependent on tool geometry. It’s done many researchs, in order to, improve FSW and optimized tools. But, for any design and optimization, it must be enough and reasonable understanding of the type of process, effective parameter and relationship.In friction stir welding (FSW), the welding tool geometry plays a fundamental role in obtaining desirable microstructures in the weld and the heat-affected zones, and consequently improving strength resistance of the joint. The geometric parameters of the tool, such as the height and the shape of the pin and the shoulder, have a great influence on both the metal flow and the heat generation due to process.Among the key components of the FSW tool geometry is the tool shoulder and the pin. In the welding of thin plate, the shoulder is the main source of heat generated during the process, the primary constraint to material expulsion and the primary driver for material flow around the tool, the pin is the primary source for material deformation and the secondary source for heat generation in the nugget. Consequently, the geometry of both the shoulder and pin are important to the FSW process. While in the welding of thick plate, addition to cited roles for thin plate, shoulder volume has essential effect on mixing and keeping softened material, as a result of further plasticized material. Hence, both pin and shoulder are sources for material deformation and heat generation during the process. Even pin is dominant in the welding of thicker plate. In this reasearch, a process with varying shoulder and pin geometries is numerically modeled. The obtained results allow finding optimal tool geometry. Because of cost and take a more time for exprimental process, it’s modelled by different pakhages. Some of these: modelling of flow pattern and heat flow. Since, we use ABAQUS-Explicit package to analysis objective process. For the cited reason, modelling divided in three stages: At the first, angle of shoulder is changed by fix pin and fix shoulder diameter about horizon. Second, pin geometry is converting to taper by change shoulder angle, instantaneously, and simulations is continued. Last in third stage, it will model by loss of shoulder volume and falatten effect by flat the outer shoulder and increase the flat effect through pin. Keywords : 1-Fiction stir welding (FSW) 2-Modeling 3-Thick plate 4-Shoulder