Objective: The preparation of liquid black garlic by lactic acid bacteria cooperative fermentation and the analysis of aroma components were studied. Methods: Fresh garlic was subjected to high-temperature enzyme inactivation at 180 ℃, then crushed and mixed with water. Different proportions of composite lactic acid bacteria were added for fermentation for a certain period of time. Liquid black garlic was prepared by high-temperature reaction at 80 ℃. The degree of browning, reducing sugar, total phenols, total acids, amino acid nitrogen content and DPPH·, ·OH scavenging rate were measured every two days using liquid black garlic (KB1、KB2) without bacterial fermentation as a reference, and the optimum conditions for preparing liquid black garlic were studied under the fermentation of complex lactic acid bacteria in different proportions, and the aroma components of liquid black garlic under these conditions were analyzed. Results: The best preparation conditions for liquid black garlic were determined as follows: The fermentation time was 9 min, the mass ratio of lactic acid bacteria S (Streptococcus thermophilus):B (Lactobacillus bulgaricus) was 3:1, and the maturation standard of black garlic was reached at 13 d. Under the same conditions, KB1 was used as the standard. At this time, the reducing sugar content was 1.20 times, the total phenol content was 1.82 times, the total acid content was 1.36 times, and the amino acid nitrogen was 1.21 times. DPPH· clearance and ·OH clearance were 1.37 times and 1.34 times, respectively. Compared with single lactic acid bacteria S and B, the thermal reaction was shortened by 2 d and 5 d, respectively. The analysis of aroma components showed that, compared with KB1, the content of thioether in liquid black garlic co-fermented by strains decreased by 54.17%, while the volatile aroma components of aldehydes and furan compounds increased by 47.98% and 6.18% respectively. The liquid black garlic basically had no garlic odor, and the aroma acceptability was better, with a sensory score of 91.38±0.98 points. Conclusion: The fermentation of liquid black garlic by complex lactic acid bacteria has a synergistic effect and can shorten the thermal reaction of black garlic, which has a good application prospect in the development and research of black garlic.