This paper investigates the substantial impact of aerodynamic interference among coaxial rotor unmanned aerial vehicles (UAVs). It establishes the theoretical correlation between the thrust generated by aerodynamic interference among coaxial rotor UAVs and the resultant thrust during operations. Furthermore, a robust flight control algorithm is developed for coaxial rotor UAVs based on a predefined aerodynamic model. The control framework combines the Time-Varying Uncertainty and Disturbance Estimator (TV-UDE) observer with a cascaded Proportion-al-Derivative-Proportional-Derivative (PD-PD) controller, effectively bridging the gap be-tween sophisticated aerodynamic modeling and practical control implementation. The effectiveness and robustness of the proposed control strategy are validated through flight simulations. Notably, significant improvements in altitude control are demonstrated, which have considerable implications for the practical application of UAVs across various fields.