There are more than 10,000 digital cryptocurrencies in the world, and they are used as a medium of exchange to a certain extent. The cryptocurrencies can be used as a medium of exchange, but due to their inherent defects, they do not have the characteristics of high-quality money, so it is difficult to become a universal mainstream currency, and can only be used in a limited field. Cryptocurrencies are not the liability of any institution or individual, nor can they be exchanged for any government fiat and commodity currencies. Therefore, in theory, cryptocurrencies are competitive private non-redeemable quasi-currencies.