The friction flow spot welding experiment has been performed on 1mm thick aluminum alloy 6061-T6.The process, microstructure and properties of welded joints were analyzed. The results show that the welded joints can be divided into four regions namely weld nugget zone, thermo-mechanical affected zone, heat affected zone and base material zone. The weld nugget zone has the tiniest grains. Down force, welding rotational speed and welding time have influences on the properties of the welded joints. In this paper, the author selects down force as the parameter for controlling the plunge depth of the tool. When down force ≤ 2300N, the hooking defeat hasn't inserted into the top surface of the upper sheet, the fracture mode acts as the “shear fracture”. When down force > 2300N, the fracture mode acts as the “plug fracture”.The study shows that when choosing down force 2300N, welding rotational speed 2000r/min, welding time 10s as the welding parameter, good weld joints of 1mm thick aluminum alloy 6061-T6 can be got.