The aerodynamic interference among rotors has strong affect on the lift force of the quadrotor UAV, it is necessary to study on the interference to provide a reference for the aerodynamic layout design. An equivalent actuator disk model of airplane propeller is presented, which takes into consideration such factors as such as diameter, chord,pitch and rotating speed of rotor, etc. The effectiveness of the equivalent actuator disk is established thorough increasing momentum source,calculating the different lift force of a single rotor in hover on Fluent and comparing with the experimental data. Thorough the above method, the effects of interference among rotors on lift force of quadrotor in hover is calculated that have different rotor distances. The resulted of the calculation indicates that the smaller rotor distance causes the stronger interference as well as the more loss of lift force.