Abstract: Time-dependent aerodynamic forces and moments of morphing aircraft during sweep-varying process are important to flight safety, and hence need thorough investigations. This paper conducted a wind tunnel experiment of morphing aircraft and analyzed the aerodynamic characteristics. The results demonstrate the dynamic hysteresis caused by sweep-varying, and various factors that affect the magnitude and director of hysteresis loop. Based on these results and some important concepts in mechanics, three physical effects, i.e., flow-field hysteresis effect, additional motion effect and wall implication effect, were proposed in order to interpret the formation mechanisms of the unsteady aerodynamic characteristics of morphing aircraft. This investigation about mechanisms can be used to further study on modeling of aerodynamic characteristics.