Cao is the official class name. The Emperor of the Western Han Dynasty placed five ministers, one of whom was called a servant, and the other four were divided into four of Cao's. The number of ministers in the Eastern Han Dynasty increased to six Cao. During the Wei and Jin Dynasties, there were 35 Cao at most, while there were only five or six ministers, so one minister was in charge of several merchants, and each merchant had one Cao. This is the origin of "Five Cao Shangshu" and "Six Cao Shangshu". Since then, Cao has been the department, and Cao's six departments have been six. Cao is the master of the Shang Dynasty, and he was appointed as a Shang Shu in the later Jin Dynasty. There are also Cao in local counties, such as Hu Cao and thief Cao, which are the themes of modern organs. In the third year of Emperor Wendi (583), Emperor Wendi changed Cao to be the division, such as the division of household and justice. Since then, local governments have stopped using Cao.