Pore-throat structure before and after strong base ASP flooding in Daqing oilfield was researched qualitatively and quantitatively using mercury injection，rate-controlled mercury injection，SEM and casting thin sections analysis. The results show that grain boundaries are dissolved and zigzag-like with unclear edges and corners，and feldspar is dissolved seriously by alkali after base ASP flooding. A large number of dissolution pores were observed. Kaolinite is dissolved and secondary quartz formed on clay mineral surface at the same time. White cloud-like scale deposits filling in pores result in changes in pore structure and partial pores are plugged. Average core throat radius dropped by 6.528% and average pore radius dropped by 3.360%. Pore-throat ratio had wider distribution and increased by 12.839% averagely. The final oil saturation was lower than that of water drive core and its final oil saturation coefficient was smaller. The residual oil saturation and ultimate oil saturation decreased with the increase of core permeability before and after strong base damage. Permeability ratio changed from 5.567 to 5.691 after the strong base ASP flooding. The stronger core heterogeneity brings more possi? bility of fingering and channeling. The poor pore throat structure will greatly influence the subsequent water flooding and the implementation of enhancing oil recovery method，and also bring about difficulties in thin and poor layers.