The wind tunnel of a 4 m-diameter coaxial rigid model rotor is conducted to investigate the aero-dynamic interaction characteristics. Both coaxial and single rotor are tested, and the upper and lower rotor forces are measured independently. The force distribution of the coaxial rotor is analyzed. The aerodynamic forces and lift offset characteristics of coaxial and single rotor are compared. Simultaneity, the free wake method is used to analyze the tip vortex wake characteristic under interference. It is shown that the coaxial rigid rotor interaction is weaken as advance ratio increases, and the coaxial rigid rotor lift offset increases due to the asymmetry aerodynamic interaction.