Abstract: With the progress of industrial technology, aerospace, transportation and other fields put forward higher and higher demand for the bearing capacity of components. In this paper, friction stir welding method was used to join 9 mm thick 2A14-T4 aluminum alloys.The microstructure and mechanical properties of high strength thick aluminum alloy plate joints along the thickness direction were studied. The results indicate that the butt joint has good appearance at the rotating speed of 400 r/min and the welding speed of 100 min/min, and the tensile strength of the joint is 360 MPa, which is 83.9 % of the base metal. There are significant differences in the microstructures of the joint along the thickness direction. The average grain diameters of the top, middle and bottom of the weld are 7.9 , 5.0and 2.8 μm, respectively. The dimples at the bottom of the joint are equiaxed, with small diameter and shallow depth. The fracture position and the minimum microhardness of the joint appear in the thermo-mechanically affected zone of retreating side. The microhardness of the top, middle and bottom of the weld are 99.9 , 97.9 and 94.7 HV, respectively.