NOVELTY - Preparing cyproterone acetate intermediate 17 alpha -hydroxy progesterone-1,4,6-triene-3,20-dione, comprises (i) adding culture medium containing glucose, corn pulp, peptone, potassium dihydrogen phosphate, GPE and water to fermentation bottle, sterilizing, adding Arthrobacter, culturing, and transferring culture medium into 1000 ml fermentation bottle; (ii) sterilizing the culture medium; and (iii) adding bacterial liquid into 1000 ml fermentation bottle, shaking, culturing, sieving, culturing by performing oxidative dehydrogenation, filtering, concentrating, filtering, and drying.    USE - The method is useful for preparing cyproterone acetate intermediate 17 alpha -hydroxy progesterone-1,4,6-triene-3,20-dione (claimed).    ADVANTAGE - The method has high selectivity microbial fermentation and dehydrogenation reaction processes; produces product without side reactions, and has purity of 97%; produces maximum impurity content of 1.5%, and increases the production yield of the product by up to 80%; and is environmental friendly, and thus it reduces the chemical production as compared with the traditional chemical synthesis process.    DETAILED DESCRIPTION - Preparing cyproterone acetate intermediate 17 alpha -hydroxy progesterone-1,4,6-triene-3,20-dione, comprises (i) adding culture medium containing 1.2-1.6 wt.% glucose, 1.8-2.6 wt.% corn pulp, 0.4-0.6 wt.% peptone, 0.4-0.7 wt.% potassium dihydrogen phosphate, 0.01 wt.% GPE and 20 ml water into a 100 ml fermentation bottle, where the pH of the culture medium is adjusted to 6-6.5 by adding sodium hydroxide, then sterilizing at 110-112 degrees C at pressure of 0.10-0.12 MPa for 20 minutes, cooling, adding 0.1% Arthrobacter, shaking at 30-33 degrees C in a rotary shaker at a rotating speed of 100-110 rotations/minute, culturing for 16-22 hours, and transferring the culture medium into 1000 ml fermentation bottle; (ii) adding all the above mentioned raw materials of the culture medium with 200 ml water into the 1000 ml fermentation bottle, and sterilizing at 110-112 degrees C at pressure of 0.10-0.12 MPa for 20 minutes, and cooling; and (iii) adding bacterial liquid into 1000 ml fermentation bottle, shaking at 30-33 degrees C in a rotary shaker at a rotating speed of 100-110 rotations/minute, culturing for 10-15 hours, sieving 1.5-2 g 17 alpha -hydroxy progesterone-1,4,6-triene-3,20-dione by 100 meshes, continuously culturing by carrying out oxidative dehydrogenation for 36-48 hours, where the conversion rate of 17 alpha -hydroxy progesterone-1,4,6-triene-3,20-dione is more than 90%, filtering the crude product of 17 alpha -hydroxy progesterone-1,4,6-triene-3,20-dione, filtering by using methanol and activated carbon, and concentrating to paste form, cooling to 5 degrees C, filtering, and drying to obtain the product.