Abstract: With increasing interests on high altitude Unmanned Aerial Vehicles (UAVs), more and moreattentions have been paid to the research of aero-engines under high altitude, low Reynoldsnumber conditions. This paper reviews the research progress on complex internal flow in low Reynolds number and low pressure turbine (LPT) in recent years. The maintopics include unsteady flow characteristics of LPT, mechanisms of separation and transitionphenomena of boundary layer, mechanisms of periodic wake/boundary layer interactions. Based on flow mechanisms, an aerodynamic design method for lowReynolds number LPT is proposed. The interactions of wake/boundary layer can inhibitseparations and diminish profile losses. Taking unsteady effects into account in the aerodynamicdesign, one can effectively improve blade loading or reduce aerodynamic losses, and finally improvethe performance of LPT. The numerical and experimental results validate this aerodynamic designmethod.