Abstract: Biological characteristics of Alternaria tenuissima in Dendrobium nobile were studied.The results showed that the suitable temperature range for mycelid growth is from 5-35℃,and the optimium temperature is 25℃.The temperature is 5-35℃ to germinate of spores,and 25℃ were optimum.Different illumination did not obviously influence to mycelial growth and spores germination.The study also indicated that the fungicides(10% difenoconazole at 67μg/mL,and 64% oxadixyl at 1607μg/mL) creat strong fungistatic action against Alternaria tenuissima in vitro,and the percentage for fungistutic action of inhibiton to the mycelial growth recorded 100%.The fungicides(90% fosetyl-aluminium) is not obvious for fungistatic action.