The invention discloses multi-flavor rainbow oatmeal meal-replacing powder and a preparation method thereof, and relates to the technical field of food processing. The multi-flavor rainbow oatmeal meal-replacing powder is prepared from the following raw materials: 50 to 80 parts of oatmeal, 10 to 40 parts of corn flakes, 0 to 30 parts of raisin, 0 to 20 parts of medlar, 0 to 20 parts of creamer, 0 to 20 parts of purple sweet potato, 0 to 40 parts of corn, 0 to 60 parts of red dates, 0 to 10 parts of matcha, 0 to 20 parts of blueberry powder, 0 to 40 parts of mung bean, 0 to 20 parts of black sesame, 0 to 20 parts of lycium ruthenicum murray, 0 to 30 parts of black rice, 1 to 10 parts of konjac flour and 10 to 30 parts of xylitol which are prepared into the meal-replacing powder of different flavors. The meal-replacing powder adopts five-color foods as raw materials for nutrition arrangement; the raw materials are clear in source, discernible, and rich in variety; the multi-flavor rainbow oatmeal meal-replacing powder can not only be pleasant to eyes to increase appetite, but also supply people with balanced nourishment, thereby ensuring the improvement on the organic health level. Long-term use of the meal-replacing powder has the effects of benefiting liver and stomach, keeping young, caring skin, and increasing immunity of a human body, and can improve the health levels of sub-health people and obese people.