Abstract: Multiple side damage (MSD) is considered a primary threat to aircraft structural safety. The experimental investigations on the residual strength of the aluminum stiffened and flat panels with multiple site damage were carried out. The panels were pre-cracked with saw cut. Each specimen was subjected to a monotonically increasing tensile load until failure occurrs and the failure load was recorded. The residual strengths of these panels in different crack sizes were obtained. Based on these experimental results, an improved model was presented in this paper. The residual strengths of those aluminum panels with multiple site damages were evaluated with the plastic zone linkup model and the improved plastic zone linkup model respectively. It was shown that for the panels with different lead crack sizes and different MSD cracks as well as different ligament lengths, the maximum errors were 53.63% and 23.08% respectively for plastic zone linkup criterion and the improved model, the average errors were 20.74% and 8.6% respectively for these two models, showing the notable improvement in prediction with the improved model.