A series of water-soluble terpolymers, poly(acrylamide/N-vinylpyrrolidone/N-(acrylamido propyl)-N,N-dimethyl,N-cetyl ammonium bromide) (ANAs), were synthesized through free radical copolymerization in water and applied for heavy oil viscosity reduction of Bohai heavy oil with high salinity. Test results showed that the solution of ANA-4 with a concentration of 1000 mg/L possesses moderate surface and interfacial activities, which could afford not only the optimal heavy oil viscosity reduction rate of 98.8% by emulsification under the high-salinity and high-temperature reservoir condition but also the fast dehydration of the formed oil-in-water emulsion within 2 h while standing at normal temperature. More importantly, dehydrated water was confirmed to be reusable with a heavy oil viscosity rate of more than 98% after 4 cycles. The mechanism of heavy oil viscosity reduction via emulsification and dehydration via demulsification was also discussed. The study provides an efficient and environmentally friendly candidate for heavy oil viscosity reduction under high-salinity conditions compared to previous heavy oil viscosity reducers.