Based on the failure criteria including COD design curves and net section yield, engineering critical assessment (ECA) on 2219 aluminum alloy structure welded by friction stir welding (FSW) was carried out. Critical crack sizes of Nugget zone (NZ), thermo-mechanically affected zone (TMAZ), heat affected zone (HAZ) and base material (BM) of 2219 aluminum alloy FSW joint were calculated. The surface defect tolerances of friction-stir-welded 2219 aluminum alloy structure under different stress-level were obtained, and ECA on longitudinal FSW joint of launch vehicle tank under a certain pressure inside the cylinder was executed. ECA method in this study provides a reference for fracture control of friction-stir-welded aluminum alloy structure. Results show that HAZ at the longitudinal advancing side is the key area for the fracture control of the 2219 aluminum alloy FSW joint. The given surface defects are acceptable under specific internal pressure