The broth derived from the natural fermentation of Vaccinium uliginosum L. at a constant temperature was used as the research object, and the microbial composition was analyzed using the plate separation technique. The isolated strains were analyzed via morphological identification and physiological and biochemical identification. The results were as follows: The microorganisms in the natural fermentation broth of Vaccinium uliginosum L. were mainly lactic acid bacteria, acetic acid bacteria, yeast and molds; the strains A1 and A2 were lactic acid bacteria, with the strain A1 being Lactobacillus and the strain A2 being Streptococcus; the strain B1 was a yeast, and the strain B1 was Kluyveromyces. The broth derived from the constant temperature natural fermentation of Vaccinium uliginosum L. was inoculated as the starting fermentation seed into the sterilized artificial fermentation substrate for fermentation. The total phenolic content and total flavonoid content were increased by 38.10% and 5.69%, respectively, and the anthocyanin and procyanidin contents were reduced by 30.22% and 31.26%, respectively, and the •OH scavenging capacity and the total antioxidant capacity were increased by 3.74% and 39.22%, respectively, compared with those before fermentation. The antioxidant capacity of the seed broth was significantly higher than that of the positive control group (p < 0.01). The ethanol content in the final product of seed fermentation was 0.98%, indicating a low alcohol fermentation product. This experiment provided a new approach for processing Vaccinium uliginosum L.