High Altitude Long Endurance (HALE) solar powered unmanned aerial vehicle has the design characteristics of low Re number which makes a great challenge to the propeller aerodynamic design. Based on the main design of a UAV, a solar powered propeller is design in this paper. Multi variables optimization method is used to design the blade element. With proper blade width and pitch distribution, the propeller works efficiently in low Re number. The propeller aerodynamic characteristics are validated in BEM method. The calculation shows the propeller has a high efficiency of over 85% in cruise.