To address the issues of poor efficiency of water flooding and low swept volume of chemical viscosity reducers for the conventional heavy oil development，a composite oil displacement system with viscosity reduction and foaming features was developed by using N，N-dimethylamine，sodium 3-chloro-2-hydroxypropane sulfonate and alkyl alcohol polyoxyethylene ammonium sulfate as raw materials. The effects of partially hydrolyzed polyacrylamide（HPAM）on emulsification and viscosity reduction of heavy oil，as well as the effects of polymer，reservoir pressure and heavy oil on the foaming ability and stability of oil displacement system were systematically investigated. The heavy oil recovery of polymer/viscosity reduction composite flooding with and without foam flooding was compared. The results showed that the introduction of HPAM improved the viscosity reduction ability of composite oil displacement systems at the lower concentrations. Under the temperature of 30—80 ℃、mass fraction of 0.3% and an oil-water volume ratio of 7∶3，the composite oil displacement system（referred to as SKY）could reduce the viscosity of heavy oil from 1607 mPa·s to 35.0—60.3 mPa·s，and then reach a high viscosity reduction rate of 96%. Meanwhile，SKY also exhibited excellent foaming performance. The stability of foam was significantly enhanced with the increase of reservoir pressure and heavy oil content. The half-life of foam increased from 8 min to 120 min when the pressure rose from 1 MPa to 13 MPa at 70 ℃. Heavy oil had obvious effect of stabilizing foam. The polymer improved the stability of foam mainly by increasing the viscosity，reducing the drainage rate of foam liquid membrane，and enhancing the strength of membrane. The physical simulation flooding experiments revealed that the polymer/viscosity reduction composite flooding system improved the recovery rate of heavy oil by 10.05 percentage points. After the injection of polymer/SKY and nitrogen，the effect of combination flooding was greatly improved. The produced foam after the injection of gas enhanced sweep efficiency during displacement，so the recovery rate of polymer/viscosity reduction/foam combination flooding was increased by 22.0 percentage points. Therefore，the viscosity reduction/ foam combination flooding technology could realize the integration of viscosity reduction and profile adjustment，which had great application prospects for enhancing heavy oil recovery by water flooding.