Alkali-surfactant-polyacrylamide (ASP) flooding technique has been used to exploit residual oil underground in high water-cut oil reservoirs. However, our knowledge about the microbial communities in ASP flooding reservoirs is sorely lacking. In this study, the microbial communities in an ASP flooding reservoir block were investigated by 16S rRNA gene sequencing, and the response of microbial populations in the ASP flooding block to nutrients stimulation were studied in laboratory.