Unified currency is an important measure in the economic field after Qin Shihuang unified the world. During the Warring States period, not only countries attacked each other, but also currencies were different. At that time, there were four main forms of money. First of all, the cloth coins shaped like shovels in agricultural tools are mainly distributed in Sanjin, namely Han, Zhao and Wei. The second is knife coins, which are mainly circulated in Qi, Yan and Zhao. The third kind is round money, which is mainly used in Qin, Western Zhou, Eastern Zhou, Zhao and Wei Yanhe (near Qin). Fourth, there are Yingcheng and Tongbei, which are only used in Chu. Countries make their own money, even private money. At that time, the disunity of currency made Qin Shihuang deeply feel that even if politics had been unified, it could not control the unification of economy. The popular currencies in the Warring States period were mainly copper coins and gold coins with different shapes. The fundamental purpose of unified currency is to consolidate political rule. The complexity of the currencies of the six countries is the concrete economic manifestation of the political chaos in the six countries. In order to establish an economic system that matches political unification, it is necessary to realize the unification of monetary policy. Qin Shihuang unified the currency mainly in two ways: first, the state unified the coinage, severely punished private coinage, and held the right to manufacture the currency in the hands of the state. The second is to unify the two currencies, namely, the upper currency gold and the lower currency copper. The change of gold is based on "Iraq", and one Iraq is 22 Liang. Copper coins take "half Liang" as the unit, and the word "half Liang" is obviously cast in gold coins. Copper coins are shaped like square holes, commonly known as "Qin Banliang". Pearl jade, tortoise shell, silver and tin used by the six countries can no longer be used as currency (when it comes to Qin, China is a second-class currency; Gold is named after Yan, and it is a coin; Copper coins, commonly known as half a tael, are as heavy as the text, and are the next coins. And jade beads, tortoiseshell, silver and tin belong to jewelry treasures, not coins-"Historical Records? Level book "). Qin Shihuang forcibly unified the currency by administrative means, which immediately and effectively controlled and standardized the chaotic situation of the monetary system in the Warring States period. Qin Shihuang's unified currency achieved much better results than unified writing. One of the important reasons is that the measures to unify the currency are more in line with the law. The size, weight, shape (knife shape, cloth shape) and value of the currencies of the six countries are different. Qin's "inner circle and outer circle" currency is more convenient to carry and circulate than the currencies of the six countries. "Qin Banliang" made full preparations for the emergence of five baht money. It can be said that "Qin Banliang" influenced the currency form in ancient China for more than two thousand years. Qin Shihuang adopted the circular currency with "inner circle and outer circle" as the unified currency form of Qin Dynasty, which is consistent with China's ancient philosophy. In ancient times, China always advocated the cosmology of "the sky is round and the place is round". Pre-Qin philosophers always thought that the sky was round and the tunnel was square. The "inner circle and outer circle" of Qin coins just conforms to this philosophical thought and is very practical. The "inside" is easy to wear, but the "outer ring" is not easy to wear. Qin's "half a tael of money and one tael of money" not only embodies China's ancient philosophy, but also has the characteristics of being easy to carry and use, so its popularity is inevitable. In addition, in the middle and late Warring States period, with the development of economy, several economic zones appeared, which coexisted with the seven warring States countries. Due to the need of communication between economic zones of various countries, the unification of currencies is gradually put on the agenda. Qin Shihuang's unified currency adapted to the inherent needs of this economic development, which is one of the important reasons for the success of this move.