Abstract: Zhazi was a very common and important document style in the Song Dynasty. It had the nature of official documents and private documents，including a group of documents with the same name but different formats and uses. In the field of official documents, it can be used as a document sent to superiors or as a document issued to subordinates. In the Southern Song Dynasty, it became a kind of private document，which could be used together with Qi for official communication or private communication.

Key words: Zhazi, document, official document, private document