Abstract: The system of monitoring county by Du You, formed in the middle of West Han Dynasty, dated back to "the legislative official supervision around the country" in Qin Dynasty and in the early of Han Dynasty. Du You supervised the activities of all feudal subjects, in particular those of officials at county level. This system showed that the local monitoring system of prefecture and county had been established in West Han Dynasty. At first, Du You was responsible to the administrative head of prefecture, irrele...