Abstract: Refilling friction stir welding process was studied in order to solve the keyhole problem of friction stir welding (FSW) of the closed ring weld of rotate-structures. In the process of refilling welding of thick plates, the problem of the instantaneous cavity at the end of the tool pin would be more pronounced and more difficult to control due to the volume effect. In this paper, the internal quality, microstructure and mechanical properties of 2219 aluminum alloy welded joints of 20-mm-thick plates with different length of refilling field were studied. The results showed that retractable friction stir welds with no internal defects were obtained with the parameter of welding speed of 100 mm/min, rotation speed of 400 r/min and the length of the refilling field of 200 ~ 500 mm. Two weld nuggets were observed on the cross section of the joint of the welding zone, and the size of the nugget near the upper surface of the weld decreased with the refilling process. The tensile properties of the one-time welding, two-time welding and refilling welding joints decreased successively. In addition, the mechanical properties of refilling welding joints increased with the length of refilling region. The refilling distance of 500 mm would a proper parameter.