Abstract: The friction stir welding of 8 mm thick 2219 alminum alloy plate was carried out, and the exposure test of the joint surface under tropical ocean atmospheric condition was carried out. The corrosion morphology and mechanical properties of 2219 alminum alloy friction stir welded joints were studied under different exposure time by using scanning electron microscope (SEM) and universal tensile testing machine.The results show that with the extension of exposure time, the tensile properties of the joint decrease. The tensile strength of the joint is 400 MPa and the elongation after fracture is 17.53% after exposure for 3 months, and the tensile strength decreases to 363.25 MPa and the elongation after fracture decreases to 15.9% after exposure for 12 months.The fracture mode develops from ductile fracture to local brittle fracture, and finally to most brittle fracture.