The cellulose modification can be made in steps, giving a range of new products having properties quite different from the parent cellulose. Effective molecular weight control and narrow molecular weight distribution of the polyacrylonitrile can be accomplished by anionic polymerization technique. Preformed polyacrylonitrile was grafted precisely onto cellulose acetate by SN$_2$ reaction mechanism in a simple and effective way under homogeneous reaction condition. The 3.5g of completely dried cellulose acetate(DS=2.4) dissolved in 50ml of dry THF was transferred to the 215m1 polyacrylonitrile solution. The mixture was stirred vigorously under nitrogen atmosphere for 2 hrs. FTIR spectra of cellulose acetate and grafted cellulose acetate were taken, and their characteristic bands were identified.