Abstract: In this paper an investigation of the ground vortex, the significant aerodynamic phenomenon in rotor aerodynamics on nap-of-the earth, is carried out. Based on the analysis of the rotor wake near the ground, a theoretical method, including the analytical model, the formulae and the computer program, has been established which can be used for calculationof the ground vortex--the longitudind position, the height above theground and its strength. By using a free wake model, with the ground vortex taken into account, the distribution of induced inflow at the r otor disc is also calculated. All computational results are compared with available experimental data and found in good agreement.