In order to supporting auxiliary power unit (APU) design
the widely used APU with load compressor in structure was discussed and modeled.Firstly
the structural characteristics and regulation law are introduced and then how the load compressor works on APU was analyzed.Finally the mathematic model of APU was established based on components.Take a kind of APU as the object for numerical simulation and then compare with the actual test data.The results show that the dynamic simulation error is less than 5%.The mathematic model of APU is suitable for engineering usage.