On August 10th, "Libra: A Financial Innovation Experiment" Reading Forum and New Book Launch Conference was held in Beijing. Economist Zhu Jiaming pointed out at the scene that the emergence of Libra allows us to understand the impact and challenges of digital currency on classical money theory and new currency theory from a larger historical perspective, and we must treat this issue with an open mind. First, the biggest problem in the history of monetary thought is the discussion about monetary neutrality. If Libra can be considered a currency, then Libra does not appear in a neutral form. In addition to the currency illusion, people are only responding to the nominal value of money, while ignoring the illusion of the change in actual purchasing power, people with bitcoin are immersed in the illusion of money every day. Regarding the question of the optimal amount of money, the theory of quantity of money is first of all the theory of money demand. But in fact, I think that the imbalance between money supply and money demand will become the biggest phenomenon in the future economy, because it is difficult to find a measure of the demand for money. Digital currency makes this problem more complicated, the currency is complicated, but this does not hinder the currency. Derivation.