Friction stir welding (FSW) is a new method that the joining is carried out by friction between two metals and heat creation. The stress concentration phenomena in welded joint cause the stress increasing in welded zone. In this research, modeling and analysis of similar junction of IN718 and Mar-M247 and non-similar junction of IN718-Mar-M247 superalloys were performed by ANSYS Software and finally the stress concentration factors of welded samples were calculated. The stress concentration factor of similar and non-similar of junctions was assessed and compared with reported experimental data in the literatures. The results showed that, the mean stress concentration factor for similar junction of Mar-M247 and IN718 superalloys are 1.566 and 1.63 respectively and for non-similar junction is equal to 1.52.