The present invention relates to a crystalline form of a BTK kinase inhibitor and a preparation method therefor. In particular, the present invention relates to a type II crystal of (R)-1-(1-acryloylpiperidin-3-yl)-4-amino-3-(4-(2, 6-difluorophenoxy)phenyl)-1, 6-dihydro-7H-pyrrolo[2, 3-d]pyridazin-7-one (a compound of formula (I)) and a preparation method. The type II crystal of the compound of formula (I) obtained by the present invention has good chemical stability and crystal form stability, and is also better used for clinical treatment as the used crystallization solvent has a low toxicity and low residues.