The invention relates to the technical field of agriculture, in particular to a biological prevention and control method utilizing cucumis melo as a trap plant to prevent and control scale insects ofa citrus orchard. The method includes following steps: accelerating germination of cucumis melo, and transplanting into the citrus orchard after greenhouse seedling culture; in the citrus orchard, foran area where cucumis melo needs to be cultivated, ploughing, sufficiently watering, covering with thin films, and cultivating cucumis melo around and between rows of the citrus orchard area, managing water and fertilizer according to those of the citrus orchard, and managing cultivation according to cucumis melo planting technology; utilizing cucumis melo to attract the scale insects, and when damaged area of whole-plant fruits, leaves and vines of cucumis melo exceeds four fifth, bagging whole damaged cucumis melo plants, putting the same onto an open cement floor for exposure to the sun for several days, and burning up. The scale insects of the citrus orchard are attracted by utilizing cucumis melo and then treated in a centralized manner, so that the number of nymphs is reduced effectively, adults and eggs difficult to prevent and control are taken into consideration, and a new way is provided for efficient prevention and control of citrus scale insects.