Abstract: In order to quantitatively evaluate the moisture state of oil-paper insulation equipment, an improved fractional Poynting-Thomson (P-T) model considering DC conductivity is established based on the concept of fractional element. Five groups of oil-paper insulation samples with different moisture content were prepared, and the frequency domain spectroscopy of the damped samples was measured. The improved fractional P-T model and the improved Cole-Cole model were used to fit the dielectric spectroscopy. The relationship between different damped samples and the parameters of the improved fractional P-T model was analyzed, and the influence of the model parameters on the frequency domain spectroscopy was studied by simulation. Finally, an example was given to verify the accuracy of the evaluation method. It is found that the improved fractional P-T model has better fitting accuracy for the frequency domain spectroscopy of oil-paper samples with different moisture degrees. With the increase of water content of oil-paper samples, the model parameters ε_b and DC conductivity increase, while the parameters ε_a and relaxation time constant decrease gradually. The model parameters ε_a, ε_b and DC conductivity have a power-law relationship with the water content, and the relaxation time constant has a linear relationship with the water content, so it can quantitatively characterize the moisture state of oil-paper insulation equipment.