The invention discloses natural yellow compound juice and a preparation method thereof. The natural yellow compound juice comprises raw materials in parts by weight as follows: 30-50 parts of oranges, 2-8 parts of lemons, 15-30 parts of carrots and 10-15 parts of papayas. The oranges, the lemons, the carrots and the papayas are taken as the raw materials, the juice contains no food additive, the four kinds of fruits are placed into a closed box for storage, environmental factors of the closed box are adjusted artificially, breathing actions of the fruits are promoted, sugar in the fruits is consumed as much as possible on the premise that other nutritional facts in the fruits are not damaged, and accordingly, the low-sugar natural yellow compound juice applicable to a diabetic patient is prepared.