The alkali ASP system was composed of petroleum sulfonate surfactant, Na2CO3 and polymer P620, P700 and P1400 with relative molecular mass 620×104, 700×104 (salt resistant) and 1400×104. When the ASP flooding weak alkali system flowed in the core of class Ⅲ reservoir of Saertu oilfield, the apparent viscosity, interfacial tension, coefficient of resistance and other parameters at different injecting stage were tested, and the change law of ASP flooding weak alkali system flooding properties in the core was obtained. The results showed that the apparent viscosity increased continuously with increasing composite system injection. When subsequent water was injected, the apparent viscosity increased first and then decreased with increasing water injection. The highest viscosity retention rate of P620, P700 and P1400 alkali ASP system was 81.53%, 17.22% and 12.05%, respectively. The interface tension of produced liquid decreased first and then increased during the conduct of displacement. The lowest interface tension of P700, P620 was 6.59×10-2 and 2.38×10-3 mN/m. With increasing injection rate of P700, P620 and P1400 ASP system, the injection pressure increased to the highest at 2.88, 0.60 and 0.87 MPa. When the follow-up water was injected, the injection pressure decreased. The resistance coefficient of P620, P700 and P1400 alkali ASP system was 75.00, 360.00 and 109.25, and the residual resistance factor of that was 22.25, 155.00 and 28.25, respectively. The injection rate of P620 alkali ASP system was the lowest when the flowing of ASP system in the core achieved stability.