Bovine milk is known as the “white blood” and is one of the most ideal natural foods, rich in protein, milk fat, calcium, vitamins and the eight essential amino acids, also known as a near-perfect food. However, in China, cow’s milk is mostly used for liquid milk processing, and its nutritional value has not been fully utilized. Casein gene polymorphisms are thought to affect milk yield, physicochemical properties and nutritional composition, dairy product manufacturing performance and nutrition, and hence have received much attention from scholars. In this paper, we summarize the existing studies on casein gene polymorphism, the methods used for its detection, and its application, hoping to provide some reference for the targeted breeding of dairy cows, the improvement of milk quality, and the precise development of functional dairy products.