Poly(N,N-diallyl-N-methylpropylammonium chloride)(PMPDAAC) was prepared by N,N-diallyl-N-methylpropylammonium chloride (MPDAAC) as monomer and 2’2-azobis(2-methylpropionamidine) dihydrochloride (V50) as initiator in aqueous solution. On the basis of single factor experiments, the Box-Behnken mathematical relational model between the intrinsic viscosity values of PMPDAAC and their affecting factors was established, and the preparation conditions of PMPDAAC were optimized. The optimum preparation conditions were: T1=56.13℃, T2=61.24℃, T3=80.22℃, w(MPDAAC)= 71.03%, w(V50)= 2.50% and w(Na4EDTA)= 0.0074%, the average value of intrinsic viscosity of PMPDAAC and conversion rate of monomer under optimal conditions reached 1.17dL/g and 92.05%, respectively. The structure of the product was characterized by FTIR and NMR, and its Mw and polydespersity d(Mw/Mn) was measured by GPC-MALLS. The results showed that the maximum Mw of the product PMPDAAC was 2.658×105, polydespersity d(Mw/Mn) was 1.358. The research showed that the space effect and possible solvent effect brought about by the substituent propyl group were the main factors affecting the polymerization activity of diallyl quaternary ammonium salt.