Abstract: In order to deeply study the complex behaviors of oil-paper insulation materials in a wide frequency band, and to achieve quantitative evaluation of the water content and aging state of related equipment, this paper integrates the dielectric modulus and fractional elements to establish a fractional model that weakens the influence of DC conductance. First, seven sets of vegetable oil-paper insulation samples with different moisture content and different degrees of aging were prepared, the frequency domain spectroscopy (FDS) technology was adopted to measure the frequency domain dielectric spectrum and convert it into a dielectric modulus spectrum. Then, the fractional model was adopted to identify the parameters, the characteristic quantities closely related to the water content ω_C and the degree of polymerization D_P were selected, and the functional relationship was established. Finally, an field vegetable oil transformer was used to measure and to preliminarily verify the effectiveness of the method. The experimental results show that the fractional model can effectively simulate the changing trend of the dielectric modulus spectrum, and the proposed characteristic parameters are closely related to moisture and aging. In the evaluation of moisture content, the characteristic parameters α, β, M_a and ω_C are power-related, and the characteristic parameter τ is exponentially related to ω_C. In the evaluation of aging degree, the characteristic parameters α, M_a, τ are power-related with D_P, and the characteristic parameter β is exponentially related with D_P.