The invention relates to an orthorhombic crystal form of compound trans-5-chloro-2,3,3a,12b-tetrahydro-2-methyl-1H-dibenz [2,3:6,7] oxepino [4,5-c] pyrrole (Z)-2-butenedioate, to methods for the preparation of this crystal form and to pharmaceutical compositions comprising an orthorhombic crystal form.本發明係關於一種化合物反-5-氯-2,3,3a,12b-四氫-2-甲基-1H-二苯并[2,3:6,7]氧呯并[4,5-c]吡咯(Z)-2-丁烯二酸鹽的斜方晶型,有關此晶型的製備方法,及包含該斜方晶型的藥學組成物。