At present, alkali-surfactant-polymer (ASP) flooding in Daqing oilfield entered into the industrial application stage and demonstrated good result in increasing oil production and decreasing water-cut. However, using the ASP system with strong base caused serious problems at some blocks and wells. The influence of alkali on the formation could complicate maintaining oil product and improving recovery. In this paper the authors investigated reactions between alkali and reservoir minerals and their effects on seepage characteristic. The research was carried out on typical core sample from Daqing oilfield. The sample were characterized by pore structure, elemental composition, resistance facto, and residual resistance factor as evaluation indices. The results showed that the reservoir rocks of typical blocks in Daqing oilfield contained alkali-sensitive mineral. The degree of alkali-sensitivity damage was evaluated as mid-weak. Compared with a weak base (NaCO3), a strong base (NaOH) could cause higher damage to the reservoir. Moreover, alkali-sensitivity damage to reservoir minerals could lead to higher injection pressure.