The invention, belonging to the technical field of medical product research and development, relates to a compound ailanthus preparation and applications thereof. The preparation is prepared by the following steps: taking ailanthus leaves, melia azedarach leaves and artemisia capillaris respectively, adding ethanol respectively, extracting under oscillation by using a shaker, centrifugating to obtain the supernatant by a centrifuge; repeating the extraction twice, mixing the supernatants obtained by three times of extraction, filtering the mixture, concentrating the filtrate by reducing pressure, drying the concentrated filtrate to obtain extracts of ailanthus leaves, melia azedarach leaves and artemisia capillaries; adding mashed garlic into a round-bottom flask, carrying out vapour distillation to obtain garlic essential oil; and taking the extracts of ailanthus leaves, melia azedarach leaves, and artemisia capillaries and garlic essential oil to prepare the compound ailanthus preparation. The preparation has bacteriostasis to fusarium moniliforme and botrytis cinerea, can be used for developing corresponding preparations for controlling plant diseases, and is suitable for industrial production.