Under the formation conditions of Wen120 block in Huabei oilfield with 87℃and 28291 mg/L salinity，the influence of effective concentration of foaming agent ，core permeability，injection speed and pressure on the residual resistance coefficient of air foam flooding was studied by single tube displacement experiment. The results showed that when the effective concentration of foaming agent increased from 0 to 0.1% ，the residual resistance coefficient of air foam flooding increased from 1 to 3.1. With continuous increase of foaming agent effective concentration ，the residual resistance coefficient increased slowly ，and then became stable. The residual resistance coefficient increased first and then decreased with increasing permeability of sand-packed model，which reached maximum ( 3.5) when the permeability was 178 × 10^-3μm². When the injection speed increased from 0.5 to 3.0 mL/min，the residual resistance coefficient increased from 2.1 to 3.3 and then decreased to 2.6. When the pressure increased from 0 to 15MPa，the residual resistance coefficient increased from 3.1 to 3.6.