The probability density of the aircraft engine oil sample spectral data was estimated by using support vector machines(SVM).According to the probability distribution of spectral data

the normal

warning and abnormal threshold of the mass fraction

mass fraction gradient and the mass fraction ratio of aircraft engine were calculated based on spectroscopic diagnosis.This method was also verified by using the actual spectral data in aircraft engine.Through comparison and analysis of the threshold based on the normal distribution assumption

it shows that the actual spectral elements of aircraft engine are not entirely subject to normal distribution assumption

so the results established by SVM-based oil-like spectral threshold method are more genuine and reliable.