The present invention relates to a crystalline form of a BTK kinase inhibitor and the preparation method thereof. In particular, the present invention relates to a type I crystal of (R)-1-(3-(4-amino-3-(4-(2, 6-difluorophenoxy)phenyl)-7-hydroxy-1H-pyrorolo[2, 3-d]py ridaz-1-yl)pyrrolidin-1-yl)butyl-2-alkyne-1-ketone (the compound in formula (I)) and the preparation method thereof. The type I crystal of the compound of formula (I) obtained by the present invention has a good crystal stability and chemical stability, and the crystal solvent used has a low toxicity and residue, thus making same more suitable for use in clinical treatment.