Abstract: Friction-stir welding of 2519 high-strength aluminum plate in 20 mm thickness was completed by a single pass.The experiment results demonstrate that when the rotating speed is 1600 r/min and the welding speed is 30 mm/min,the weld's tensile strength reaches 313 MPa.The frictionstir weld softens becouse the welding speed is slow,and the length of the soften zone is 55 mm,and the microhardness in the stir zone is about 115 HV on the average.The fracture mode is ductile and brittle mixed fracture.The temperature difference of the stir zone through thickness is about 150℃.Becouse of the change of temperature and force through thickness,it is very difficult to weld plate when the thickness is large.