The new gray prediction NGM (1,1,K) model has a problem of mismatch between the defined type and the white type.In order to eliminate the inherent deviation caused by the mismatch problem,an extended NGM (1,1,K) model was proposed,and the prediction formula of the model was given.The model was used in the fitting and prediction of the elemental concentration value of the spectral analysis of the hydraulic system in a certain type of excavator,and a high accuracy was obtained.The predicted value combined with the threshold value of the spectral analysis element concentration value can effectively predict the future operating state of the hydraulic system,achieve active maintenance,and ensure the reliable operation of the hydraulic system.