Abstract: The traditional method for determining the total acid content of vinegar is the titration method, which is complicated, time-consuming, and has high requirements for operators. A rapid method of the determination of total acid content in vinegar by Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) was established. The acid substance in vinegar was carboxylic acid, and the carbonyl groups in carboxylic acid had a characteristic peak around 1 710 cm^-1. There was a good linear relationship between the peak intensity and the total acid content of vinegar. The total acid content of 15 kinds of vinegar samples was determined. The results determined from the established ATR-FTIR method was consistent with those from the national standard method (GB/T 12456—2008), and the correlation coefficient (R) between them was 0.997 6; the relative standard deviation (RSD) among the results of 9 replicate determinations was less than 1% (n=9), and the limit of detection (LOD, s=3) was 0.042%, which indicated that ATR-FTIR method could be used for the rapid determination of total acid content in vinegar. Meanwhile, the method is easy to operate, fast, and has a wide range of applications. It can be used for laboratory research, vinegar production, storage and transportation, and large-scale follow-up testing of production enterprises.