In this work,based on the continuous heating measure by DXR laser microscopic Raman spectrometry,the change regulations of the Raman feature peaks of ester base oils,such as trimethylolpropane trioleate（TMPTO）,tridecyl trimellitate（TDTM） and dioctyl adipate（DOA） were investigated under online heating condition.Changing characteristics of ester oil molecular structure during the thermal oxidation process were studied.The results showed that some Raman peak positions and Raman intensity of ester oil varied with the increase of heating temperature.The C—H stretching vibration peak of methyl and methylene and the shear vibration peak of methylene of ester base oil are very sensitive to temperature.With the increase of temperature,the peak intensity has different degrees of weakening but could basically recover after cooling down.There is no obvious variation on C‖O vibration peak with the increase of temperature.The C‖C stretching vibration peak position of TMPTO ester base oil gradually shifts to higher wave region with the increase of temperature and will recover after cooling.Under the isothermal condition,the Raman intensity of TDTM base oil has no obvious change,the Raman intensity of C—H stretching vibration peak of methylene of DOA ester base oil and the Raman intensity of ‖C—H,C‖C and—CH2— of TMPTO ester base oil decrease with the increase of oxidation time.Therefore,in situ Raman spectroscopy could be used to monitor the continuous thermal oxidation process of unsaturated ester oils,but it has some limitations in the monitoring of high temperature oxidation of saturated ester oil and aromatic ester oil.