This research uses Illumina high-throughput sequencing method showing that dominant phylum of dried oily wastewater reservoirs (DOWRs) in oilfield were Proteobacteria, Actinobacteria, Bacteroidetes, and Carbohydrate Metabolism presented a major proportion of metabolic activity. Core microorganism analysis showed that Mycobacterium, Altererythrobacter, Dietzia, Pseudoxanthomonas, Melioribacter were the key genus, which were important in maintaining the microbial construction and function, and which can be treated as the key bio-stimulation community. [ABSTRACT FROM AUTHOR]