The invention discloses a red bean and grain pulp drink and a preparation method thereof. The drink consists of grain pulp and oat in a weight ratio of 9:1, wherein the grain pulp comprises the following components in percentage by weight: 0.5 to 2 percent of roasted peanut, 0.5 to 2 percent of polished round-grained rice, 0.5 to 2 percent of purple rice, 0.5 to 3 parts of red bean, 6 to 8 percent of white granulated sugar and the balance of water. The red bean and grain pulp drink is prepared by the following steps of: grinding and cooking to form the grain pulp, adding treated oat into the grain pulp, and bagging. The red bean and grain pulp drink is formed by the following steps of grinding the polished round-grained rice, the purple rice, roasted peanuts and red beans and cooking to obtain the grain pulp with moderate viscosity and adding the granular oat, contains amino acids which are rich in the polished round-grained rice and the red beans and are essential to human bodies, and also has the characteristics of various nutrient components such as calcium, phosphorus, iron, B vitamins and the like and the nutrition characteristics of the oat and the peanuts; and the drink hassoft and smooth mouthfeel and rich nutrition.