Extracting method for abamectin B1a

The invention relates to an extracting method for abamectin B1a. The extracting method is characterized by comprising the following process steps: first, filtering abamectin fermenting liquid by adopting a micro-filtration membrane to obtain abamectin-rich membrane paste; then, extracting the membrane past by using a compound solvent; next, adsorbing by using an aluminium oxide chromatographic column and desorbing by butyl alcohol after the obtained extracting liquid is concentrated; collecting desorbing liquid of a B1 stage, de-colouring, filtering and performing primary crystallizing to obtain abamectin B1 crude product; re-crystallizing through ethyl acetate to obtain a finished product with high content of the abamectin B1a. According to the extracting method, the abamectin is extracted in the mode of adopting micro-filtration membrane and compound solvent extracting and combining an aluminium oxide chromatographic column and butyl alcohol desorbing process, so that the abamectin and the product quality c