Counties in Tang Dynasty were assigned into four, five, six, seven, eight, ten, etc. tiers according to household registration, official rank, salary rank, transfer order and other different standards. From a diachronic point of view, the county tiers were constantly increasing from six tiers in the early stage to ten tiers in the later stage. One exception was during the Tianbao years, the lowest tier of counties was cancelled. However, the designations of Wang (望), Jin (紧), Ci Chi (次赤) and Ci Ji (次畿) counties had no direct relationship with the number of registered permanent residents, but rather reflected more if the county was fertile or barren. Among them, the problem of Ci Chi county was particularly complicated, because it can be interpreted in both broad and narrow senses. However, a comprehensive analysis shows that the system of Ci Chi county had already appeared in the early years of Daizong Period at the latest. The salary rank formed from the late Daizong Period to the early Dezong Period had a new impact on the county tiers in the late Tang Dynasty and Five Dynasties. In Five Dynasties, the county tier was determined by the number of registered households, although different dynasties had different standards, either complicated or simple. In summary, in the Tang Dynasty and the Five Dynasties, the criteria for county tiers changed from official rank to salary rank.