Objective: To control the medicinal plant diseases with the preparation of Trichoderma harzianum., Method: Antagonistic action of the preparation to the pathogens of the medicinal plants in vitro, and controling effects of the preparation on these diseases in greenhouse and in the field were tested., Result: The test in vitro showed that Trichoderma harzianum, used as a biocontrol factor, had stronger antagonistic action to Fusarium equiseti, Sclerotinia sp. and Rhizoctonia solani which were the medicinal plant pathogens of Astragalus membranaceus, Glehnia littoralis and Panax quinquefolium respectively. Biological controling effects on sclerotium root rot of Glehnia littoralis were 83.6% and 72.5% respectively in greenhouse and in the field with the preparation of Trichoderma harzianum. And controling effects on root rot of Astragalus membranaceus and seedling damping-off of Panax quinquefolium were 80% and 60% respectively in the field. The dosage of the preparation used in the field was 10 g.m-2., Conclusion: The preparation of Trichoderma harzianum can be used as a substitute for such chemicals as Carbendazim. Using the preparation to control medicinal plant diseases provides a technical safeguard for the good agricultural practice of medicinal plants.