Cold recovery by viscosity reduction is an important method as for heavy oil exploitation. In this work, a kind of amphiphilic block polymer viscosity reducer HPAM/AOS was synthesized. As well as high surface activity, a large number of polar groups in hydrophilic blocks impose it strong emulsifying ability and heavy oil affinity, thus to improve the viscosity reduction effect effectively. Meanwhile, the emulsifying ability of HPAM/AOS for heavy oil was determined by spinning drop interfacial tensiometer, electrical stability tester and laser particle size analyzer, accompanied by Zeta potentiometer for affinity information. To be specific, compared with HPAM, the oil-water interfacial tension of HPAM/AOS emulsion decreased by 98.2% to 0.007 mN.m^-1, and the demulsification voltage increased by 104.9% to 420 V. Furthermore, in comparison with AOS, the absolute potential of HPAM/AOS emulsion Zeta is reduced by 75.3% to -17.8 mV, proving its more affinity to heavy oil. Generally, the viscosity reduction ratio of HPAM/AOS is increased by 74.2% and 48.7% respectively compared to HPAM and AOS, showing its good treatment efficiency.