In　order　to　achieve　high　efficient　operation　between　the　APU　and　the　whole　vehicle,　control　system　of　the　auxiliary　power　unit　has　been　developed.　The　structure,　function,　and　working　principle　of　the　auxiliary　power　unit＇s　control　system　have　been　introduced.　The　control　system　of　auxiliary　power　unit　adopts　the　INTEL　16　bit　microcontroller　to　its　control　kernel　and　estimates　the　battery　pack＇s　SOC　by　inspecting　the　battery　pack＇s　voltage　and　the　current.　When　the　SOC　is　below　the　set　value,　the　engine-generator　system　starts　running　at　a　steady　revolution　and　chargs　the　battery　pack.　The　auxiliary　power　unit＇s　control　system　can　judge　the　auxiliary　hybrid　electric　vehicle＇s　working　model,　and　drive　the　LCD　mounted　in　the　vehicle　to　display　the　vehicle＇s　working　model　and　battery　pack＇s　voltage　and　current　value.