It is difficult to increase crude oil production for Daqing oil field by conventional technologies. In order to increase crude oil production, we make use of microbial enhanced oil recovery technology. The results showed that fluid production increased by 11 tons, oil production increased by 1.7 tons, water rate has decreased by 0.6 tons in oil reservoir after polymer flooding, North-2-4-P47 single-well daily. Microbial community diversity and dynamic change in oil reservoir after polymer flooding in Daqing Oil Field, North 2-4-P47 single-well in the process of microbial enhanced oil recovery was analyzed by PCR-DGGE. The results showed that the dominant microbes of North-2-4-P47 single-well are Acinetobacter johnsonii., Pseudomonas fluorescens., Pseudomonas sp., Bosea sp., Syntrophothermus lipocalidus., Aeromonas media. and some uncultured bacterium. Overall, microbial community diversity is abundant, and dynamic change of microbial community is also great in North-2-4-P49 single-well.