In the early years of the State，Nguyen Dynasty followed the port tax system of the chua Nguyen regime，and levied “Full-coin” port tax on foreign merchant ships. Under the situation of increasing “shortage” of silvers and “shortage” of coins，and based on the consideration of “general use of silvers in China and general use of coins in Vietnam”，as well as the removing disadvantages of coins，Nguyen Dynasty began to levy “Half-silver and Half-coin” port tax on foreign merchant ships in 1803，that is，half of the port tax coins was converted into silvers and the other half was levied with coins. The “Half-silver and Half-coin” port tax was initially implemented during the Gia Long period，and was fully and strictly implemented since the early years of the Minh Menh period. This tax levied by the Nguyen Dynasty on the Qing merchant ships，mainly Guangdong merchant ships，reflects the asymmetric relationship between the amount of “Half-silver” and the amount of “Half-coin” in most cases. It has the dual characteristics of “rigidity” and “flexibility”. Its in-depth implementation finally brought Vietnam into the world silver circulation circle.