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