<,正,>,Amphiphilic star-block copolymers composed of polystyrene and poly（acrylic acid）were synthesized by iodide- mediated radical polymerization.Firstly,free radical polymerization of styrene was carried out with AIBN as initiator and 1,1,1-trimethyolpropane tri（2-iodoisobutyrate）as chain transfer agent,giving iodine atom ended star-shaped polystyrene with three arm chains,R（polystyrene）,3,.Secondly,tert-butyl acrylate was polymerization using polystyrene obtained as macro-chain transfer agent,and star-block copolymer,R（polystyrene-b-poly（tert-butyl acrylate））,3, with controlled molecular weight was obtained.Finally,amphiphilic star-block copolymer,R（polystyrene-b-poly（acrylic acid））,3, was obtained by hydrolysis of R（polystyrene-b-poly（tert-butyl acrylate））,3, under acidic condition.