The common aromatic polyamide composite reverse osmosis (RO) membrane is easy to be oxidated. 2,2-difluoro-1,3-diaminopropane (DFPDA) as a key functional monomer can be used to prepare the chlorine resistance composite reverse osmosis membrane by interfacial polymerization technology. In this study, DFPDA was synthesized through a three-step reaction including fluorination, amidation and reduction. The diethyl malonate as substrate was first reacted with the fluorination reagent of selectfluor to get the first intermediate 2,2-difluoro-diethyl-malonate(DFDEM), then the DFDEM was amidated by ammonia water to prepare the second intermediate 2,2-difluoro-malonamide(DFMA), and lastly the resulting DFMA was further reduced via boron hydride (BH3) to obtain the final product DFPDA. The reaction technologies of three steps including fluorination, amidation and reduction were investigated, and thereinto the fluorination technology was optimized through orthogonal test, at the same time the fluorination mechanism was discussed. The chemical structures of all products were identified via infrared spectra (IR), hydrogen nuclear magnetic resonance (1HNMR) and mass spectragraph (MS). This current method for preparing the DFPDA has several advantages, including the accessible substrate, mild reaction condition, safe operation and relatively high yield.