Hydrolyzed protein formula not only solves the problem of allergy or intolerance to cow’s milk proteins in infants and young children, but also meets the nutritional needs. Degree of hydrolysis is an important parameter to evaluate hydrolyzed protein formula. However, there are currently no methods available to determine the degree of hydrolysis of hydrolyzed protein formula. This article presents a brief introduction to the basic concepts of hydrolyzed protein formula and its degree of hydrolysis, and summarizes the existing methods for detecting the degree of hydrolysis of proteins. We expect this review to provide a reference for the establishment of detection methods for the degree of proteolysis of hydrolyzed protein formula.