Friction stir welded butt joints were performed on sheets made of AA2024-T351 aluminum alloy at tool rotational speeds of 400, 630, 800 rpm and traverse speeds of 8, 16, 25 mm/min. The fatigue crack propagation rate was investigated according to standard ASTM-E647 in CT specimens. FE simulation of FSW process was implemented for different welding conditions and next the fatigue crack propagation was simulated using XFEM method. In this analysis, to assess the damage in the joints, maximum stress criterion is used. The maximum principal stress in element was the fracture criterion. Numerical results are in good agreement with the experiments so the simulation is reliable. The obtained results show that the tool rotational and traverse speed affect the fatigues crack growth rate. For all welded specimens crack propagation rate was slower than that of the base metal for low values of ∆K (∆K≤13 Mpa) but is much faster at high values of ∆K. Furthermore fatigue properties of specimens that welded with lower speeds are better than base metal and increase in rotational or traverse speeds of the tool will increase the crack propagation rate of the welded specimens.