Abstract: The single-pass friction stir welding (SPFSW) of 2219 aluminum alloy plates with thickness of 8 mm was carried out, while the dual-pass (DP) FSW was performed for 2219 aluminum alloy plates with thickness of 15 mm. The FSW thermal process and tensile property of 2219 aluminum alloy with different thickness were comparatively investigated.The influence of second pass welding on the microstructure and tensile property was emphatically studied. It is found that the high-temperature zone and the maximum temperature during the DPFSW process are both bigger than those of the SPFSW process. The maximum temperature of the advancing side is slightly lower than that of the retreating side. Besides, the tensile strength of the DPFSW joint with thickness of 15 mm is slightly lower than that of the SPFSW joint with thickness of 8 mm. The tensile fracture mechanism of the joints is the mode combining the dimple aggregation fracture with cleavage fracture.