Abstract: In order to research the crack propagation behavior of friction stir welded joints of 2219 aluminum alloy, the tests on mechanical properties and ductile crack propagation of the joints were conducted. Based on the results of P-V curves in different areas of friction stir welded joints and the crack tip opening angle (CTOA) values at different crack lengths, the crack propagation resistance and the crack propagation direction were studied. The results indicate that the crack propagation resistance in different areas of weld joint of 2219 aluminum alloy was greater than that in base metal under the research conditions, and there were no obvious differences in crack propagation resistance at the center of weld seam, thermo mechanically affected zone (TMAZ) on advancing side and retreating side. The inhomogeneity of the microstructure and mechanical properties of the joints led the instability of crack propagation directions. the cracks in TMAZ of advancing side propagated in the direction of weld seam, and the cracks in weld seam deflected toward TMAZ of retreating side, and the cracks in TMAZ of retreating side and in base material propagated with minor deflection.