The low molecular weight polymer of poly(N-vinylformamide) was synthesized by precipitation polymerization in N,N-dimethyl formamide and ethyl acetate, using azobisisbutyronitrile as the free radical initiator and dodecyl mercaptan as the chain transfer agent. The influences of monomer mass fraction, component solvent ratio, initiator concentration, chain transfer agent concentration, reaction temperature and time on the precipitation polymerization were investigated. In the optimum conditions, the polymer was obtained with 93.1% yield and the number average molecular weight (Mn) of the polymer was 2975.2 with PDI of 2.64 and the polymerization residue could be recycled . Then the polymer was hydrolyzed to poly(N-vinylformamide-co-vinylamine) with different amination degree in the hydrochloric acid solution. The hydrolysis products with the number average molecular weight of 1000~1400 and PDI of 1.34~1.40 were obtained.