CHUN QIU HISTORY BOOK recorded: CHI country's courtier CHUI ZU murdered his monarch KUNG. Confucius recorded the event that the courtier CHUI ZU murdered monarch KUNG in CHUN QIU HISTORY BOOK. Confucius had the recording rule in the book about murdered matter. His record rule was: When courtier murdered monarch, if it was fault by monarch, he should wrote the monarch's name. If it was the courtier's guilty, he should wrote the courtier's name. When monarch was murdered by courtier, Confucius didn't write the murder's name, It means: the monarch was killed by all people. he was a bad monarch. On the other hand, if Confucius wrote the murder's name, it means: it was the courtier's guilty. He wanted everybody knew who killed the monarch. According to the record regulation, CHUI ZU's name was written in the book, maybe Confucius thought that CHUI ZU had guilty. But when we studied ZUO'S Commentary, we could find the reason why CHUI ZUI killed the monarch. The reason was: monarch was promiscuous with CHUI ZU wife, many people knew the ugly thing. This matter let CHUI ZU feel embarrassed and difficult. CHUI ZU was angry. He murdered the monarch at last. In fact, Chi's monarch was promiscuous. His behavior was incorrect. The result was that he was murdered. CHUI ZU killed his monarch KUNG. This matter had happened that had its background. CHUI ZU couldn't endure monarch KUNG's inapt behavior. The proposal of this paragraph was that based on ZUO's Commentary and other historical books to clarify the history event. To research the real reason and progress for this murdered event. We can find some different meaning between CHUN QIU HISTORY BOOK and ZUO'S Commentary.