The invention relates to a hydroxypropyl -sulfo butyl -ª‰-cyclodextrin and its preparing method, analysis method and the applying in medicine, wherein the hydroxypropyl -sulfo butyl -ª‰-cyclodextrin is the cyclodextrin derivation displaced by hydroxypropyl and sulfo butyl. The n-(2, 3, 6-O-2-hydroxypropyl )-m-(2, 3, 6-O-sulfo butyl)-ª‰-cyclodextrin, each mole cyclodextrin displaced group number is n hydroxypropyl and m sulfo butyl, wherein n is the average displaced degree of the hydroxypropyl displaced group; m is the average displaced degree of the sulfo butyl displaced group; n+mú¢Z is the total average displaced degree; nú¢any of the 1,2,3,4,5,6, 7,8,9; m=any of the 1,2,3,4,5,6, 7,8,9; z=any of the 1,2,3,4,5,6, 7,8,9,10.