Disclosed are crystalline forms 1, 2, and 3 of a selective S1P1 receptor agonist, namely Ponesimod, and a method for preparing the same. An X-ray powder diffraction pattern of the crystalline form 1 has characteristic peaks at 2 theta values of 18.1° ± 0.2°, 14.6° ± 0.2°, and 11.3° ± 0.2°. An X-ray powder diffraction pattern of the crystalline form 2 has characteristic peaks at 2 theta values of 3.8° ± 0.2°, 10.8° ± 0.2°, and 6.1° ± 0.2°. An X-ray powder diffraction pattern of the crystalline form 3 has characteristic peaks at 2 theta values of 12.2° ± 0.2°, 6.2° ± 0.2°, and 5.6° ± 0.2°. Compared with existing crystalline forms, the present invention has better stability and a greatly increased solubility, and is more suitable for development of a pharmaceutical preparation containing Ponesimod
