The invention discloses a preparation method of collar of a formula I, which comprises the step of performing a reaction of a compound VII in alcohol solution of ammonia to remove protective groups R1 and R2 of hydroxyl, wherein R1 is benzoyl and R2 is benzoyl or acetyl; and the alcohol solution of the ammonia is C1 to C4 alkyl alcohol solution of ammonia, which contains 1 to 35 weight percent ofammonia. The invention also discloses a preparation method of the intermediate compound VII of the collar. The preparation methods of the invention has the advantages of short reaction time, high yield, high final product purity, low production cost, simple operation and easy industrial promotion.