Abstract: Through analysis of the characteristics of four typical flight stages of solar powered unmanned aerial vehicle (UAV) in the air, the power models required are summarized in this paper. Based on these models, it is concluded that the power required is closely related to total mass, power factor, and aspect ratio. The influence of these factors on energy system and overall design are analyzed. By studying the relationship between power factor and angle of attack, the range of angle of attack which meets the flight energy requirements is obtained. Considering the energy balance, the models of each subpart mass and total mass of solar powered UAV are established. Besides, the influence of wingspan and aspect ratio on mass is examined. Simultaneously, the relationships among the mass of battery, solar cells, and power demands are discussed. Based on the analysis, it is concluded that with the increase in wingspan, the power required of solar powered UAV increases. When the wingspan is constant, the power required decreases as the aspect ratio increases.