The key properties of cellulose insulating paper are regulated by fiber morphological structure. To elucidate the correlation mechanism between fiber morphology, structure, and performance and achieve accurate prediction of insulating paper properties, this study utilized unbleached softwood kraft pulp as raw material. Paper samples were prepared by controlling beating degree. Through characterization techniques including fiber quality analyzer, polarized light microscopy, and X-ray diffraction, we quantitatively analyzed the influence of beating degree on fiber morphology and structural parameters such as fiber length and fibrillation rate. Using tensile strength and power-frequency breakdown strength as representative mechanical and electrical performance indicators, multiple linear regression models were constructed via the best subset method. The models demonstrated that fibrillation rate and air permeability dominantly influence tensile strength, while fiber length and thickness significantly affect breakdown strength. Validation results showed prediction relative deviations of less than 10% for tensile strength and under 5% for breakdown strength, confirming high predictive accuracy of the models.