Self-reacting friction stir welding (SRFSW) is an advanced variant of friction stir welding (FSW) and shows several superiorities with the double-sided tool configuration. Despite the considerable amount of experimental studies in this field, most of the tool development efforts are still empirical and resort to trial-and-error solutions. To reveal effects of tool features on process physics and guide tool designs, in this study, a multi-physics SRFSW process model is developed within the framework of computational fluid dynamics (CFD). A shear stress boundary condition is applied at the tool-workpiece contact interface. First, the velocity distribution at weld cross section are calculated and the results show that the threads on the pin contribute to the enhancement of stirring effect. Second, the temperature evolutions at advancing side (AS) and retreating side (RS) are compared, and position in RS has higher temperature than position in AS accordingly. Finally, the plastic strain distribution behind pin tool is calculated by integrating effective stain rate along pathlines. The result shows that AS has a more definable strain boundary than RS, which corresponds to the general macroscopic observations in SRFSW. The results may provide a reference on SRFSW tool design.