In the fifth year of founding ceremony, Emperor Wu of the Han Dynasty (1 18 BC), "it made the county state cast five baht of money, so that Zhou could not crush it." This monetary reform has two characteristics. The first is to set the weight of money at five baht. In the process of currency evolution of other civilizations in the world, the weight of metal currency finally stays at around five baht, which shows that the Han government has finally found the most reasonable weight of metal currency after a long period of exploration, so that its face value is consistent with its actual value. Secondly, the anti-counterfeiting technology of coins has been significantly improved. In the past, coins were only engraved on one side, so that thieves could grind copper sheets without surface to make coins, while five baht coins added one side to the surface without words, making it impossible for people to grind copper sheets and make new coins. Casting five baht, the currency value is the same, and the copper mine has been nationalized at this time. By preventing the polishing of copper scraps, the source of copper materials for thieves is cut off, and folk theft is effectively put an end to. However, there is still a flaw in this monetary reform. The right to coin is not in the central government, and five baht is minted by counties. County officials cut corners when minting coins for local interests, resulting in five baht not reaching the specified weight. Therefore, this reform did not completely solve the currency problem in the Han Dynasty. In the fourth year of Emperor Ding Yuan (1 13 BC), he carried out the last monetary reform in the period of Emperor Wu. In the second year of Ding Yuan, a captain Shuiheng was appointed to be in charge of Shanglin Garden, and his subordinate officials included Lian Sheng, Guan Zhong and Tong Bian, the so-called Shanglin Three Officials. In this reform, the right to coin was first returned to the central government, and local counties and towns were completely banned from casting money, and the Linsanguan was specially ordered to cast five baht; Secondly, it is ordered that only the money of the three officials can be circulated in the market, and all the money previously cast by local counties and countries will be invalidated and melted, and its copper will be transferred to the three officials in Shanglin. In this way, the central government has completely controlled the right to coin. Because the five baht money cast by Shanglin Sanguan has good color and sufficient weight, and copper scraps are difficult to grind, it is not cost-effective to steal this money privately. Therefore, "the people cast less money, the cost is incomparable, and the practice of big thieves" basically put an end to the phenomenon of stealing casting.
Qin Shihuang unified the currency, while Han Wudi only carried out reforms.