The invention discloses a polyhydroxy polyamine surface activity initiator and a preparing method thereof. A tri-tert amine compound containing polyhydroxy group and cetyl group is synthesized and is made to have the characteristics of a surfactant; meanwhile, redox reaction can be conducted between tertiary amine and potassium persulfate at normal temperature, cation free radicals are formed on nitrogen atoms firstly and then converted into carbon free radicals at adjacent positions, free radicals can be generated repeatedly under flexible control, multiphase tandem connection polymerization can be achieved, polymerization between styrene and methyl acrylate and polymerization between styrene and acrylamide are triggerned on a water/oil interface in sequence, and a corresponding segmented copolymer is obtained; experiments prove that the rate of charge of a monomer is quite consistent with the component ratio of the copolymer, which implies that the ignition efficiency of the initiator is high. The polymerization reaction condition of the mode is mild and controllable, energy consumption is low, no other organic solvent or emulgator is used, the product is pure, and the requirement of green chemistry is completely met.