The invention discloses a method of planting sugar orange trees on a mountain slope. The method comprises the first step of preparation before planting, the second step of planting, wherein sugar orange tree seedlings are sequentially planted in different cement frame sets from bottom to top along the mountain slope according to successively increasing heights, and the third step of fertilization, wherein one month after the sugar orange trees are planted, a plurality of spherical gelatin sponges are placed nearby roots of each sugar orange tree seedling. According to the method, the mountain slope with the gradient between 36 degrees and 43 degrees and the orientation to the south is selected, the sugar orange tree seedlings with different heights are sequentially planted in different cement frame sets from bottom to top along the mountain slope according to successively increasing heights, the sugar orange tree seedlings are distributed in a step shape, it is guaranteed that all the sugar orange tree seedlings can enjoy sunlight within the maximum range, sunlight exposure is more sufficient, the sweetness of sugar oranges is improved, and the problem that the quality of sugar oranges is lowered because leaves on the lower sides of the sugar orange trees cannot be exposed to sunlight and illumination is uneven when the sugar orange trees are planted on flat land is avoided.