Abstract: In order to improve the precision of model identification,direct identification algorithm for a second-order plus zeros and dead-time(SOPZ/DT) continuous system is deduced based on the step response data.According to the step response data of the mini auxiliary power unit(APU),system model was identified based on the proposed algorithm.The simulation has been done based on the identified model and the simulation data compared with the test data.The results proved that the identified model has high precision and can be treated as the control model.