As the main lifting system of ducted coaxial multi rotor aircraft, the ducted coaxial propeller has the advantages of compact structure, high aerodynamic efficiency, low aerodynamic noise, safety and reliability, etc. To further improve its power load and wind resistance, the numerical simulation method is used to calculate and analyze aerodynamic characteristics of coaxial ducted propeller in hover, axial and oblique flow states. The main lifting system configuration of air leakage ducted propeller is proposed, and its aerodynamic characteristics are discussed. Compared with the ducted coaxial propeller, the superiority of the air leakage ducted propeller is given.