TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Method: The method comprises accessing short growth culture medium in Acanthospermum atherinidae and C. blakesleeana AS 3.910 spore suspension; and culturing for 1-3 days at 25-30 degrees C to obtain pre-culture system, in which 1 liter growth culture medium comprises (g) glucose (0-40), yeast extract (1-5), peptone (2-5), and potassium nitrate (1-5) and has pH of 6.0-7.0, and that accessing volume of A. atherinidae and AS 3.910 spore suspension of inoculation culture is 10-50 ml/l. It preferably comprises accessing spore concentration to grow in culture medium at 1x 106 to 1x 108/ml C. blakesleeana AS 3.910 spore suspension to obtain pre-culture system for culturing for 2 days, in which 1 liter growth culture medium comprises (g) glucose (40), yeast extract (5), peptone (5), and potassium nitrate (5) and has pH of 6.5, and accessing volume of A. atherinidae and AS 3.910 spore suspension of inoculation culture is 20 ml/l. It may comprise accessing phosphate buffer solution containing glucose in C. blakesleeana 3.910 wet cell AS to obtain pre-culture system, in which pH of phosphate buffer solution is 6, glucose is 1-3 mass%, and C. blakesleeana AS 3.910 of wet cell inoculation is 100-250 g/l phosphoric acid buffer solution. The transformation reaction is performed at 28 degrees C and conversion is performed for 4 days. The pre-culture system is added with betulin solution into table conversion reaction at 120-200 revolutions per minute. The separating and purifying step comprises transforming liquid supernatant, adjusting pH of supernatant at 3-4, extracting with ethyl acetate, and concentrating extraction liquid to obtain betulic acid. Preferred Component: The betulin solution comprises betulin at 7-9 mg/ml dimethyl sulfoxide solution, such that betulin is 0.03 g/l in pre-culture system. The pre-culture system is further added with 0.1-1 vol.% surface active agent.    TECHNOLOGY FOCUS - POLYMERS - Preferred Component: The surface active agent is Tween-80 (RTM: Polyoxyethylene (20) sorbitan monooleate) at 0.1 vol.% of solid in pre-culture system.