The present invention relates a crystalline form of androgen receptor inhibitor and a preparation method thereof. In particular, the present invention relates a type I crystal of (S)-4-(3-(4-(2,3-dihydroxypropoxy)phenyl)-4,4-dimethyl-5-oxo-2-thioxoimidazolidin-1-yl)-2-(trifluoromethyl)benzonitrile(formula I) and a preparation method thereof. The preparation method comprises 1) heating any crystal form or amorphous compound of formula (I) in a sufficient quantity organic solvent to obtain a solution, then cooling the solution to cause crystallization； said organic solvent is one or more of a solvent selected from the group consisting of ethyl acetate with no more than five carbons, acetone, nitrile, ether； 2) filtering, washing, and drying the crystals obtained in step 1). The type II crystal of compound of formula (I) obtained by the present invention has a good chemical stability and crystal stability, and the used crystal-solvent has a low toxicity and residue, which can be better used in clinical treatment.本發明涉及一種雄性激素受體抑制劑的結晶形式及其製備方法。具體地，本發明涉及(S)-4-(3-(4-(2，3-二羥基丙氧基)苯基)-4，4-二甲基-5-羰基-2-硫酮基咪唑啉-1-基)-2-(三氟甲基)苯甲腈(式(I)化合物)的I型結晶及其製備方法，所述方法包括：1)將任意晶型或無定型的式(I)所示化合物加入適量的有機溶劑中，加熱溶清後冷卻析晶，上述有機溶劑選自碳原子數小於等於5的酯類、酮類、腈類、醚類的任意一種或它們的混合溶劑；2)過濾結晶並洗滌，乾燥。本發明所得到式(I)化合物的I型結晶具備良好的化學穩定性和晶型穩定性，並且所用結晶溶劑低毒低殘留，可更好地用於臨床治療。
