Abstract: The reaction of vanillin with sorghum tannins can form a more stable red compound. Using this experimental principle, spectrophotometric determination of tannin in sorghum was established. At the same time, procyanidins were used as a standard for replacing catechins, which were commonly used as a standard for the vanillin assay, and the extraction conditions and reaction conditions were optimized. The results showed that results obtained by using procyanidins as a standard was closer to the true content of tannins in sorghum. Under strong acid conditions, the color of vanillin and sorghum tannins changed significantly. The recovery rate of the method was 74%~110%, the average standard deviation was 0.00~0.03, and the variable coefficient was 0.00%~6.67%. The vanillin method was not only sensitive, specific, but also simple and rapid. It can be used as an effective means for determining the tannin content in sorghum.