Numerical simulation is carried out to calculate and analyze the aerodynamic interaction between the front rotor/fuselage/rear rotor during the tilting and transition state of the cross shaped four-rotor UAV. The calculation models of isolated front rotor, front/rear rotors, front rotor/fuselage, and front/rear rotors fuselage combination are established. Numerical calculation and analysis of aerodynamic force and aerodynamic torque of the front rotor/fuselage/rear rotor at the different angles of rotor tilting are proposed. It is concluded that the front rotor is the leading factor in the aerodynamic interference of the whole UAV in the front rotor/fuselage and front/rear rotor fuselage combination. It provides the theoretical guidance for the design and optimization of the configuration of this kind UAV.