Abstract: In order to explore the unsteady aerodynamic characteristics and the mechanism of morphing wing during span-varying process, numerical simulations were conducted for a model of ONERA M6 wing based on dynamic mesh technology, and its unsteady aerodynamic characteristics were studied. The results show that, as the hysteresis loops, the unsteady aerodynamic characteristics curves of morphing wing during shape morphing are surrounding the corresponding quasi-steady curves; that morphing period, angle-attack and stream Mach number have some influences on the loops. But compared with the corresponding quasi-steady, the unsteady aerodynamic characteristics caused by variable span are not significant; under certain numerical condition, the maximum of unsteady lift coefficient deviation from the corresponding quasi-steady is less than 2%. The main reason of the above unsteady aerodynamic characteristics is flow field structure hysteresis. Meanwhile, the unsteady aerodynamic characteristics of variable-span morphing wing are not significant due to the weak flow field structure hysteresis.