The role of the propeller in a distributed propeller/wing configuration were investigated based on the momentum source method which translates the role of the propeller into the role of the blade force distribution. Firstly, the feasibility and efficiency of the momentum source method for solving the aerodynamic force of the configuration were verified by comparing different numerical simulation methods. Then, the key factors of the propeller slipstream affecting the aerodynamic force of the rear wing were investigated by varying the trend of the blade force distribution. Finally, the effect brought by the change of propeller height was analyzed. The results show that a propeller with a more uniform distribution of the blade force enhances the slipstream around the hub and facilitates the expansion of the low-pressure area on the upper surface of the rear wing, which has the beneficial effect of “increasing lift and reducing drag”. The rotation of the slip-stream causes an uneven distribution of the aerodynamic force across the wing span, which has the effect of “increasing lift and reducing drag” on the upper wash side and is the key factor affecting the aerodynamic force of the wing. In addition, an appropriate increase in propeller height can further increase the lift and lift-to-drag ratio of the wing.