As the development of avionic technology, the utility management of the aircraft electromechanical system has played the important role. Research in influence factors of the pressure drop of the filter has the important guiding significance for reasonably determining the warning pressure drop. In this paper, through the effect of oil contamination level on pressure drop, established a model of the oil contamination level and pressure drop, which can predict the lifetime of filter. The practicality and correctness of the established model have been verified through simulation to establish the hydraulic system filter warning system.