Abstract: In order to study the performance of 3A21 and 6063 dissimilar aluminum alloy friction stir welding joint，sixteen groups of different welding parameters are chosen for friction stir welding experiment．During the experiment，to study the mechanics performance at the welding line，the width at the welding line of the welding joint under test is narrowed to make the tensile break at the welding line．The distribution laws of the hardness and the tensile strength of the 6063-O/3A21 welding joint and 6063-T6 /3A21 welding joint with the welding velocity，the rotation velocity and the ratio of the welding velocity to the rotation velocity are analyzed according to the test data and suitable parameter range is obtained． Results show that the friction stir welding joint with good mechanics performance can be obtained if the suitable welding parameters are chosen． The friction stir welding joint meets the engineering application requirement．