A synthesis method of azidocellulose nitrate by chemical interaction between cellulose nitrates or chlorocellulose nitrates with various degree of chlorination with sodium azide in a medium of dimethylsulfoxide and with heating in the temperature range 40–70 °C is proposed. The chemical composition, structure and properties of the obtained compounds are determined on the basis of combination of physico-chemical methods of analysis: IR, 1H NMR and 13C NMR spectroscopy; elemental analysis; gel permeation chromatography; viscometry; thermogravimetric analysis; differential scanning calorimetry; thermal polarization microscopy. The main directions of the chemical interaction between polymers and sodium azide were predicted by quantum-chemical methods using the Gaussian 09 software. The reaction mechanism was confirmed by a mathematical model of kinetics. The scheme of the preferred simultaneously going reaction directions has been composed, which includes substitution of nitrate groups by the azide fragment; rupture of polymer chains by β-glycosidic bond leading to depolymerization; opening of the glucopyranose cycle with addition of the azidogroup to the formed free bonds. Use of the chlorocellulose nitrate for the azidation allows to get products with a higher degree of substitution by azidogroups, and the rate of azidation of chlorocellulose nitrate depends on halogen content directly.