The invention discloses a novel substance, namely hexahydro-1-sulfo-3,4-diaza-cyclopentane[cd] indene-4-ketone and a synthesis method thereof. The method for preparing the novel substance comprises the following steps: sulfonium salt or (3aS,6aR)-1,3-dibenzyl-4-(3-ethoxypropyl)-tetrahydro-4H-thieno[3,4-d]imidazole-2(3H)-ketone and a hydrogen bromide solution are heated to reflux, then cooled to be between 90 and 100 DEG C, added with a solvent to be stirred, and layered immediately, and an acid water layer is subjected to vacuum concentration and is cooled; and solid phosgene is dissolved by the solvent and then is dripped into the aqueous solution, then an acid water layer is recovered, and absolute ethyl alcohol is added into the mixture to precipitate a white solid, namely the target product. The hexahydro-1-sulfo-3,4- diaza-cyclopentane[cd]indene-4-ketone provides the comparison of impurities in a pure product for the measurement of impurity content in biotin, thereby improving the quality of the biotin.