Provided are an L-proline compound of a sodium-glucose cotransporter 2 inhibitor, and a monohydrate and a crystal of the L-proline compound. Specifically, provided are 1,6-dehydrated-1-C{4-chloro-3-[(3-fluoro-4-ethoxyphenyl)methyl]phenyl}-5-C-(hydrox ymethyl)-²-L-idopyranose L-proline (a compound of formula (I)), a monohydrate and an A-type crystal thereof and a preparation method therefor. The obtained A-type crystal of the compound of formula (I) has good chemical stability and crystal stability, and a crystallization solvent used has low toxicity and low residue, so the A-type crystal can be better used in clinical treatment.
