In this article, the external digestion of konjac tofu mixed with starch was studied by simulating oral, gastric and small intestine digestion, and the remaining part of the digestion was used as a substrate for in vitro fermentation of mouse cecum, and its fermentation performance in the cecum was studied. The results showed that pure konjac tofu was not digested in the mouth, stomach and small intestine, and the konjac tofu mixed with starch could be partially hydrolyzed in the mouth and not hydrolyzed in the stomach, most of the hydrolysis can be completed within 20 min. But compared with pure starch, the rapidly digestible starch of the starch incorporated into konjac tofu was reduced, the total hydrolysis rate did not change significantly. It shows that deacetylated konjac glucomannan can delay starch digestion, but can’t prevent starch digestion. In the process of cecal fermentation, the ability of konjac tofu with starch to decrease pH is higher than that of pure konjac tofu, but the short chain fatty acid and lactic acid bacteria content produced by fermentation for 24 h by the former are less than the latter. It is indicated that eating konjac tofu with starch will rapidly raise blood sugar and reduce the intestinal probiotic effect of konjac tofu.