The invention discloses a method for preparing cycloastragenol by means of biological conversion and degradation of astragaloside. The method is characterized in that astragaloside serves as a substrate, and cycloastragenol is prepared by means of fermentation of the strain of Absidia sp.CGMCC 3.2834. According to the method for preparing cycloastragenol by means of biological conversion and degradation of astragaloside, a microbiologic fermentation technology is adopted for degrading astragaloside to obtain high-purity cycloastragenol, the technology is simple and easy to carry out, the cost is low, the conversion rate of cycloastragenol reaches 60% or above, the purity reaches up to 95% or above, and the conversion specificity is high; the whole technological process is conducted at normal temperature and atmospheric pressure, the required equipment conditions are low, and the method is suitable for mass production.