To explore the digestive characteristics of oat protein isolate and cholecystokinin (CCK) secretion-promoting activity of its digesta, oat was used as raw material to extract oat protein isolate by alkaline extraction and acid precipitation in this study. The relative molecular weight change, nitrogen release and amino acid composition of digesta of oat protein isolate in the simulated gastrointestinal digestion process were analyzed, and the amino acid score, chemistry score and essential amino acid index was calculated. The CCK secretion-promoting activity of digesta was evaluated using STC-1 cells model. The results showed that after oat protein isolate was digested, the relative molecular weight of digesta was less than 10 kDa, and the proportion of soluble nitrogen released increased to 90.11%. In the soluble part of gastrointestinal digesta of oat protein isolate, the proportion of free amino acids and peptides were 22.8% and 67.31%, respectively. The relative molecular weight of peptides was mainly below 1000Da (about 74%). The total amount of essential amino acids in the gastrointestinal digesta of oat protein isolate accounted for 38.75%, the ratio of essential amino acids/non-essential amino acids was 0.63, and essential amino acid index (0.95) was greater than 0.90. The results from STC-1 cells indicated that the digesta of oat protein isolate could significantly promote the STC-1 cell growth, and increase the synthesis and secretion of CCK. These results indicated that as a high-quality protein, oat protein isolate not only had excellent nutritional functions, but also exerted the biological activity of promoting CCK secretion. Oat protein isolate might have great application potential in the food field.