Preparation of low molecular weight distribution polyvinyl pyrrolidon

The invention discloses a preparation method of polyvinylpyrrolidone with low molecular weight distribution. The method uses azobisisobutyronitrile (AIBN) or benzoyl peroxide (BPO) as an initiator, FeCl or CuCl as a catalyst, and triphenyl phosphine (PPh3) as an organic ligand, to obtain the polyvinylpyrrolidone (PVP) polymer with low molecular weight distribution, under constant temperature condition by the reversed atom transfer radical polymerization (RATRP) in the noumenon of monomer N-vinyl pyrrolidone (NVP), with maximum conversion of monomer up to 90 percent. The invention overcomes insufficiencies of using poisonous organic macromolecule halide-substituent as the initiator by traditional atom transfer radical polymerization (ATRP), being easy oxidation of low valence metal salt and harsh of reaction conditions, and the like, replaces the macromolecule halide-substituent with common free radical as the initiator, and replaces the low valence metal salt with stable high valence metal salt, thus having e