High Altitude Long Endurance (HALE) Solar UAV is integrated with a series of motor-propeller propulsion systems along the large aspect-ratio wing. These systems have an obvious effect on the flight dynamics of the UAV. This paper established a model for the interaction between distributed propulsion systems and the flight dynamics of the airplane, it was used to improve the computation of the UAV’s flight quality, results with and without the modified model were compared. It was found that the large aspect-ratio wing integrated with distributed propulsion systems can change its stability significantly. According to the result, parameters of the propulsion systems are adjusted to optimize the flight quality and system efficiency.