Ivermectin,22,23-dihydroavermectin B I.are used worldwide in livestock production and in health care of animals.It is currently synthesized by chemical reduction of the double bond between C22 and C23 of avermectin B 1 produced by Streptomyces avermitilis using rhodium chloride as a special catalyst for region-specific hydrogenation[1].This process is expensive,and causes heavy metal pollution.