Considering the characteristic of flight data's multimode, a new method for monitoring the trend of parameters aiming at aircraft health status evaluation is proposed. First, the filtering process, jump-point elimination and statistic analysis to the flight data are performed during the steady - working state and typical - flight period. Then, by using AR model the value of the parameters is predicted, and finally by using the threshold value comparison method the trend of parameters is monitored successfully. The result shows the accuracy and applicability of this method.