Aimed at the difficulty of heavy oil development and the process of emulsification and viscosity reduction ，theself-emulsifying system with polymer nonionic block polyurethane surfactants as the main agent was developed. The polymer nonionic block polyurethane surfactant （DBPS）was synthesized，and the critical micelle concentration was2.71× 10^-6mol/L. The effect of initiator （Na₂CO₃）dosage and different emulsifier and auxiliary surfactant on the emulsification and viscosity reduction of heavy oil was studied. The optimum formula was obtained by orthogonal test: 0.5% Na₂CO₃，0.5% DBPS，0.5% Tween-80and 0.6% polyethylene glycol. After self-emulsifying system and heavy oil was mixed ，dispersed oil-in-water emulsified oil droplets was developed. The emulsification viscosity reduction rate was above98% ，the dehydration rate reached 73% after2.5 h sedimentation at 80℃，the surface tension of self-emulsifying solution was 27.02mN/m at 70℃，and the interfacial tension between self-emulsifying system and heavy oil reduced to0.0057mN/m