A Tibetan corpus is constructed and annotated for the syllable markers,the word boundary markers and the part-of-speech(POS)tags,with texts selected from Tibetan textbooks of Primary and middle school.Then an empirical study reveals that the training data with the multi-level annotation can enhance the effects of POS tagging. Due to the strong relation between the POS tags of words and the tags Tibetan syllables,a method of Tibetan POS tagging by the Tibetan syllables is presented.The results of experiments show that syllable tags can correct certain errors caused in POS tagging.