A well-defined graft polymer cellulose and poly butyl methacrylate was synthesized by atom transfer radical polymerization with cellulose –Br which was synthesized by2 – bromopropionyl bromide and cellulose in ionic liquid[AMIM]Cl, CuBr and PMDETA as initiating system , DMF as solvent. The macroinitiator and polymers were confirmed by means of FTIR , 1H-NMR and GPC. The experiment studied the polymerization activity and the impact on polymer molecular weight and molecular weight distribution by time, catalytic systems ,solvent and other characteristics. The results show that reaction conversion rate increased linearly with time, the process is active and controlled polymerization, the reaction process used PMDETA / CuBr and DMF is more efficient.