To address the problem of structural fatigue failure at the constraint locations caused by dynamic loads exceeding tolerance limits at the constraint points in full-scale aircraft fatigue tests, the main factors contributing to dynamic load imbalance at the constraint points are studied. The excitation-response characteristics of multi-channel coordinated loading control and the structural dynamic load response process are analyzed. It is revealed that the coupling between the excitation-response phase difference of the control system and the structural dynamic response is the primary cause of the imbalanced dynamic load at the constraint points. Based on the fundamental principle of damping control, an elastic damping constraint method is proposed, and an elastic damping constraint device is designed. The feasibility of the method is demonstrated through structural strength analysis, flow field analysis and transient dynamic simulation, and the optimal ranges for key design parameters are determined. The method and device are validated in the full-scale fatigue test of a certain aircraft model. The results show that the elastic damping constraint effectively reduces the dynamic load imbalance during testing. The research findings are widely applicable to the full-scale fatigue tests of other aircraft models.