Money is not a system, but a common name for money. Money is the product of a certain stage in human history, and it is the historical necessity of the development of human productive forces to a certain stage, the emergence of surplus products and the exchange of surplus products. Due to the phenomenon of surplus product exchange, human beings have the demand for equivalents. Gold and silver, because of their great value, easy preservation and hard loss, finally won out among various equivalents and became the universal equivalent, namely currency. It has five functions, the most important of which is the value scale and the medium of exchange. With the development of human economy, paper money has appeared. Paper money is the symbol of money and is issued by virtue of the state's compulsory force. Therefore, money is an economic category as well as a historical category. It is the product of a certain stage of mankind. According to Marx's classical theory, money is a commodity economy phenomenon. When human productivity develops to a certain stage, human economy develops to product economy, and human distribution mode develops to distribution on demand, the phenomenon of money will disappear, that is, gold and silver are no longer money.