Abstract: In order to reveal the influence of the complex near-ground boundary on the time-averaged aerodynamic response of the ducted coaxial rotor, the steady-state RANS method and the RNG turbulence model were used to study the effects of ground height (h/D = 0.1～5.0), ground inclination angle (α = 0°～60°) and relative position of the steps (l/D = −1.5～1.5) on the lift distribution of the duct and the upper and lower rotors, and the public rotor ground effect test data was used to verify the numerical method. The results show that as h/D decreases, the ducted lift decreases while the upper and lower rotor lifts increase; when h/D = 0.1, the lift gain ratios of the three are approximately 0.28, 1.60 and 1.58 respectively. For the h/D = 0.6 operating condition, when α increases from 0° to 60°, the ducted lift gain ratio increases from 0.910 to 0.964, and the upper and lower rotors decrease from 1.050 and 1.045 to about 1.000, indicating that the lateral drainage formed by the inclined ground can weaken the ground's constraint on the exit wake. In the step condition, after the aircraft axis crosses the edge of the step (l/D from negative to positive), the ducted lift gain ratio drops from about 0.88 to 0.65, and the upper and lower rotors increase to about 1.17 and 1.10 respectively. The jet divergence, deflection and rewinding near the edge lead to the redistribution of the lift of the components. The above-mentioned three types of near-ground boundaries, ground height, ground inclination angle and relative position of the steps respectively reflect boundary distance constraints, boundary direction changes and local geometric mutations. Their effects are the reconstruction of the exit wake organization and duct pressure distribution, and further lead to the redistribution of lift between the duct and the upper and lower rotors; based on this, a unified physical link of "boundary conditions-average flow field-pressure distribution-component lift" can be established. The steady-state RANS modeling system in this paper realizes a unified comparison of the average flow structure and component lift under complex near-ground boundaries. Strong ground effects and step edges can be used as key conditions for subsequent unsteady research, which can provide a basis for near-ground aerodynamic performance evaluation of ducted coaxial rotor and subsequent control modeling.