Abstract Preparation of new chloromethylation reagent- Chloromethoxy butane(CMB) with butanol,paraformaldehyde and dry hydrogen chloride as raw material was reported in this paper.The product was confirmed by FTIR and 1H-NMR. Effects of the volume of solvent, molar ratio of reactants, reaction temperature and reaction time on the reaction have been studied. The optimal reaction conditions obtained by orthogonal test were solvent 1,2-dichloroethane 50 mL, n(CH3CH2CH2CH2OH) : n(CH2O) =3:2.00, reaction temperature 0-5℃, reaction time 7 h. Under these conditions, the yield of Chloromethoxy butane(CMB) can reach 92%. The product was used to chlomethylate crosslinking polystyrene(10%divinylbenzene crosslinking). Chlorine content highest reach 13% which is detected by Volhard method.