The selective oxidation of nitrogen dioxide in $CCl_4$ for regenerated cellulose to C6 oxidized regenerated cellulose (ORC) was proved using FTIR and NMR, and the ORC were dried under three different conditions, including vacuum-dried at high temperature, air-dried at room temperature and frozen-dried at low temperature. The degrees of polymerization (DP) of ORC gradually decreased with the increase of the oxidation time, which was probably due to the decarboxylation reaction. The DP of ORC further decreased and the color became deep as the increase of drying temperature, which was probably due to the ${eta}$-elimination reaction from C2 or C3-carbonyl group, and the yellow color of ORC was due to chromophoric enol structure. The final DP was determined by two kinds of degradation process based on the oxidation of C6 and little C2 or C3, respectively.