Wind energy is expected to play a key role in achieving the green energy transition, as offshore wind turbine technology advances quickly, offshore floating VAWTs have drawn a lot of attention. Under the action of wind and waves, the motion and torque of the floating offshore VAWT undergo periodic changes and generate additional aerodynamic loads. In this paper, the aerodynamic characteristics of a Counter-Rotating Double-Impeller VAWT (CR-DI-VAWT) under longitudinal oscillation and longitudinal rocking motions are investigated based on STAR-CCM+. First, key structural parameters such as the number of blades and impeller radius are optimized by the CFD method and the Taguchi method. Then, based on the optimized Single-Impeller VAWT model, the aerodynamic performance of the DI-VAWT under different rotor spacing L conditions is analyzed. Finally, the effects of longitudinal oscillation and longitudinal rocking motions with different amplitudes and periods on the aerodynamic characteristics of the DI-VAWT were investigated using the customized functions in STAR-CCM+. It is found that the power coefficient of wind turbines can be affected to differing degrees by variations in rotor spacing, longitudinal oscillation motion, and longitudinal rocking motion. These findings will provide a reference for the design and optimization of OF-VAWT.