By comparing the advantages and disadvantages of several different aerodynamic theories for propellers, the strip theory is applied to predict the performance of propeller at the primary design station of propellers, and the Multiple Rotating Reference Frames (MRRF) method based on solving the N-S equations is applied to evaluate the aerodynamic performance of propeller. The validation of the MRRF method is against the experimental data of a propeller. The comparison of calculated result with the experimental data shows that, the MRRF method used in this paper is reliable to predict the aerodynamic performance of propellers. The cruise altitude of Solar Airplanes is usually very high, so the Reynolds numbers of the propeller sections are very low. The key factor of the aerodynamic design of the propeller is that how to keep the propeller at high cruise efficiency by the output power restriction of the electromotor. The analysis of the designed propeller shows that the cruise efficiency of the designed propeller is no lower than 70%, and the power required at the best cruise efficiency condition is match for the rated output power of the electromotor.