Abstract: Graft copolymerization of acrylamide（AM）and acrylic acid（AA）onto cassava starch was conducted in a five-component inverse emulsion system with potassium permanganate as initiator. Effects of reaction temperature and time，concentrations of initiator and monomer，the ratio of AM to AA on the graft percent and graft efficiency were investigated. Structure of the obtained St-g-AM/AA ternary copolymer was characterized using Fourier transform infrared spectroscopy（FTIR）and scanning electronic microscope（SEM）. Results illustrated that all the factors of reaction temperature and time，initiator and monomer concentrations，and the AM to AA monomer ratio showed predominant influences on the graft copolymerization. FTIR and SEM analysis proved that graft copolymerization reaction occurs at the starch particle surface，and both PAM and PAA have been successfully grafted onto the starch molecules.