In order to sufficiently realize the functions of Auxiliary Power Unit (APU) to an aircraft, it is very important to design a good APU control system. This paper was a research on the APU aircraft level control system design and discussed the aspects which should be considered when control subsystems were designed, such as APU control panel, APU controller power supply, fuel control, emergency stop, APU air bleed, starter/generator, air inlet door control and indication/warning, etc. Some examples of design were provided and detailedly analyzed from the perspectives of function realization and electrical principle. This paper provided a recommendation for outline design and detail design of APU aircraft level control system.