Abstract: To realize the alternation between flight phases in flight simulation of maintenance training devices, processing line model was established and corresponding state control algorithm was proposed for nonlinear time-varying systems. The algorithm accurately mapped the state of the research object to the material position on the processing line, by which solved the state transition problem of complex nonlinear time-varying systems on the premise that the state deduction was feasible. The algorithm was proved to be able to realize the alternation between flight phases in flight simulation, satisfy the needs of aircraft maintenance experiments and training, and provide a reference for state transition of nonlinear time-varying systems with similar requirements.