The hP’ags-pa script was created in the late 13th century (the early Yuan dynasty) which was intended to transliterate all the languages of the Mongol empire such as Tibetan, Uyghur and Chinese into a single writing system. Among all the Chinese hP’ags-pa materials, the primer Bǎijiā xìng 百家姓 [Surnames of the Hundred Families] (BJX) offered us extensive hP’ags-pa syllables and their corresponding Chinese characters. The BJX in hP’ags-pa script has four editions that are currently known to scholars. A careful comparison and examination of the four editions of the BJX text reveals three main types of errors in hP’ags-pa syllables: (1) The misuse of similar-looking letters; (2) Pure clerical errors; and (3) Errors in the transliteration of variant pronunciations. The variant transliterations in the C edition provide some clues to sound changes, including (1) The devoicing of voiced stops and fricatives and (2) The loss of the bilabial nasal coda [m]. Aside from the variant transliterations, the majority of errors are purely graphic and reflect a lack of knowledge about the writing system. An examination of the use of the hP’ags-pa script in the BJX text suggests several potential reasons for the failure of the script to come into common use. These include: (1) A misconception of the nature of the hP’ags-pa writing system; (2) An ineffective learning approach; (3) The discrepancy of phonological categories and phonetic values; and (4) The non-adaptability to the Chinese language.