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Polyhedral oligomeric silsesquioxane (POSS) has eight substituent groups, which can be substituted with various substances to obtain different modification effects. In order to study the effect of different substituents on the modification of cellulose by POSS and its internal mechanism, the pure cellulose model and the modified cellulose with three kinds of POSS derivatives, polyoctamethyl silsesquioxane (PMSQ), polyoctaphenyl silsesquioxane (PPSQ) and polyoctaaminophenyl silsesquioxane (OAPS), were established by molecular dynamics method. The thermal stability parameters and polarizability were calculated. The simulation results showed that different POSS derivatives can improve the thermal stability of insulating paper cellulose, and the modified effect of OAPS is the best. Compared with the unmodified model, the glass transition temperatures of the modified cellulose models of PMSQ, PPSQ and OAPS increased by 58 K, 63 K and 71 K, respectively. The mean square displacement of the modified models is significantly reduced, and the free volume is increased. The addition of POSS derivatives increase the entanglement between the cellulose chains, and compresses the gap between the cellulose molecular chains to suppress the movement of the cellulose chain. It is also found that the addition of POSS derivatives can effectively reduce the polarizability of cellulose, even the electric field distribution in oil paper insulation system, so as to enhance the insulation of transformer.