Disclosed are a hydrochloride salt crystal of a drug (Filgotinib) for treating or preventing a JAK-associated disease and a preparation method, pharmaceutical composition, and formulation thereof, and an application of the hydrochloride salt crystal, the pharmaceutical composition, and the formulation in the prevention and/or treatment of a disease associated with a JAK family kinase. In comparison to a known crystal, the crystal provided in the invention shows more favorable properties in terms of pharmaceutical engineering, such as higher stability under low water activity conditions, simplicity in the preparation process and/or higher solubility.
