Abstract: The performance and control strategy of diesel-electric auxiliary power unit (APU) is restricted by the basic performance of the diesel engine and the generator. Some key parameters play the main role, such as the ability of speed regulation for the diesel, the variance ratio of speed and the change rate of generator torque. Firstly, a test bench for APU was built and these key parameters were tested to get the boundary value of Diesel and generator, establishing a basis for optimization of the control strategy.