Objective To explore and utilize the abundant lactic acid bacteria resources in nature, promoting the industrial production of traditional Chinese sour soup.Methods Lactic acid bacteria were isolated from naturally fermented foods and raw materials, identified by morphology, Gram staining, and 16S rDNA sequencing, and screened based on their microbial growth characteristics for high acid yield and acid resistance. Sour soup was prepared using these strains as the fermenting agents, and the total acid content and color difference were measured. The fermentation process was optimized using single-factor and response surface methods.Results Lactic acid bacteria such as Limosilactobacillus fermentum, Pediococcus acidilactici, Lactiplantibacillus plantarum, and Lacticaseibacillus paracasei were isolated from samples, including Xiangxi sour soup. Among these, L. paracasei LK10 (LK10) with strong acid-producing ability and L. fermentum T1 (T1) with good acid tolerance were selected. Using LK10 and T1 as the fermenting agents, the optimal process conditions were determined as follows: adjusting the OD_{600 nm} of the seed liquid to 1.00, with a volume ratio of LK10 to T1 at 5∶1, a total inoculation amount of 4.23 mL/100 g, and fermentation at 37 ℃ for 9.75 days. Under these conditions, the total acid content of the sour soup was (19.43±0.12) g/kg.Conclusion The sour soup prepared with L. paracasei LK10 and L. fermentum T1 has a moderate sour and spicy taste, a bright red color, and a rich lactic acid flavor.