Abstract: Frequency domain spectroscopy (FDS) is considered as a promising insulation assessment method which attracts extensive attention. Temperature normalization process occupies a fundamental position in the workflow of insulation evaluation based on the FDS and will eventually determine the accuracy of its insulation evaluation results. To establish an effective and accurate temperature normalization method, by in-depth understanding of complex permittivity physical meaning, we propose a novel dielectric response mechanism analysis method comprising the first-order partial differential equation of frequency spectrum and the joint analysis for real and imaginary parts of complex permittivity, which can realize the separation of independent microscopic processes of conductance, low frequency polarization, and high frequency polarization. Furthermore, FDS curves with a series of testing temperatures for oil-paper with different insulation conditions are analyzed, by which the respective temperature characteristics of independent processes are quantitatively observed and their barrier heights are extracted. The experimental results show that the temperature-dependent characteristics of those dielectric processes are significantly different, and they jointly decide the temperature shift characteristic of macroscopic FDS curve. On this basis, a broadband method for temperature normalization of FDS of oil-paper insulation based on the thermodynamic characteristic parameters of each independent microscopic process is established in this paper, which has clear physical meaning, complete process steps and is applicable for material spectrum analysis and field insulation evaluation.