The invention discloses a method for planting garlic, black garlic and a method for preparing black garlic. The garlic is planted in a plateau region, a plateau region has a large temperature difference between day and night, the garlic does not get sick easily, is free of environmental pollution and is green and environmentally friendly, pests can be prevented from the root cause, the nutritionalvalue of the garlic is improved, the produced garlic is rich in quality, the garlic growth vigor is good, and the yield is high. In the black garlic prepared by adopting the method, no chemical substance needs to be added, the fermentation time is short, the black garlic having high nutrient ingredients can be prepared, and the black garlic has no spicy taste, no odor and no irritating odor and emits sweet and sour flavor; the black garlic prepared by the method has strong bactericidal anti-inflammatory effects and anti-tumor effects and prevents cardiovascular and cerebrovascular diseases, food fibers in the nutrient ingredients in the black garlic can be chelated with cholesterol, so that the absorption of cholesterol by the human body is inhibited, and cardiovascular diseases such as hypercholesterolemia and arteriosclerosis can be prevented and controlled.