Abstract: Based on the property of Fe (Ⅲ) with thiocyanate and tannin can occur specific reaction to form a stable three element metal ionic compounds, a new method for the determination of tannin in sorghum grain sorghum was established. The results showed that the color of liquid changed significantly after the reaction of ferric thiocyanate and tannin, and there was an obvious absorption peak at 575nm. Under the optimized conditions, the concentration of tannins between 0. 001 ⁰. 06g / L was obeyed the Lambert-Beer ' s law. Correspondingly, the regression equation was Y=13.664X+0.0389, and the correlation coefficient R2was 0.9993. The average recovery of this new method was in the range of 95.77%¹01.60%, and the RSD<1%. This new method was used to determined tannins content in sorghum samples, and the results were consisted with national standard test method (GBT 15686-2008) . The method, which is simple, rapid, high sensitivity, specificity and strong anti-interference ability, can be applied to the sorghum tannins rapid detection and identification of sorghum varieties.