In the high speed situation, the efficiency of propeller drops rapidly after design point with the performance of the propeller deteriorated sharply, and the high altitude long endurance (HALE) unmanned aerial vehicles (UAVs) are difficult to meet the design requirements for fast climbing and rapid maneuvering. The swept blade design method was used to solve this problem. Five swept blades were designed on the basis of unswept blade, and the sweep angles were 10°, 20°, 30°, 40°, and 50°. Three dimensional Reynolds averaged Navier-Stokes(RANS) equations were solved based on periodic boundary condition, and multiple reference frames(MRF) model was employed to simulate the aerodynamic properties of unswept and swept blades. According to the results, the reason why the efficiency of propeller drops rapidly after design point was discussed firstly, and then the thrust, power and efficiency of different blades were compared. Moreover, the influence of swept design of blades was discussed through comparing the pressure distribution on each blade. The results show that the decreasing attack angle of blade with the increasing of flight speed as well as the tip compression effect of blade lead to the rapidly dropping efficiency of propeller after design point. The decreasing attack angle of blade can be avoided by changing the propeller rotational speed according to the changing of flight speed, however, the tip compression effect of blade always effected the propeller performance negatively no matter what the advance ratio is. The comparison of the thrust, power and efficiency between different sweep angles show that, the swept blade can provide higher thrust but need more power, and the high-speed performance of propeller is satisfactory when the sweep angle is between 30° and 50°. The comparison of the pressure distribution between different sweep angles shows that the performance of swept blades is influenced by the changed attack angle and the three-dimensional tip effect of the blade. The comparison of the tip pressure distribution between swept and unswept blades shows that the strength of the tip shock wave can be reduced by the swept blade method, but the interference of the shock wave/boundary layer contributes to the strength. In conclusion, the swept blade design method can reduce the impact of the tip compression effect on propeller, but the swept blade performance is influenced by the changed blade attack angle, the three-dimensional blade tip effect, the strength of the tip shock wave, and the shock wave/boundary layer interation.