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This work is a computational study of the low Reynolds number aerodynamics for MAV applications. The emphasis of the research is to design the optimal MAV model that has a simple geometrical structure but superior in its performances. For a better understanding on the low Reynolds number flow structures, this work started with an investigation of the laminar separation bubble (LSB) on both a two dimensional aerofoil and a three dimensional wing planforms, including rectangular, trapezoidal, Zimmerman and inversed-Zimmerman wing planforms. The fuselage effects on aerodynamics were also studied, and it degraded the overall aerodynamic performance due to the aerodynamic interaction between the wing and fuselage. However, it improves the overall static longitudinal stability for all wing planforms. The aerodynamic comparisons show that the Zimmerman wing-fuselage model has a better static longitudinal stability than other models. The propeller slipstream effects for the Zimmerman wing-fuselage model was also carried out. The overall aerodynamics is improved. The swirl flow from the propeller, however, modifies the overall flow structure on both the upper and lower wing surfaces. The LSB forms on both the lower wing sides (a long bubble is formed on the down-going blade side, and a short bubble is found on the up-going blade side). Flow separation takes place at both sides of the fuselage. The longitudinal stability margin improves almost twice than that on the isolated wing-fuselage model. The static lateral stability shows that the MAV without the vertical stabilizer is statically laterally unstable, whereas the MAV with vertical stabilizer is statically laterally stable. Finally, the fluid-structure interaction effect on aerodynamics for the Zimmerman wing-fuselage model is also investigated, showing that the separation region on the upper wing surface is reduced significantly due to wing flexibility. This results in a significant upwards shift of the lift curve, with a much higher CLmax. The flexible wing also shows a longer working range for lift than the rigid wing model. In other words, the flexible wing model has the capability to carry more payloads.