The central bank currency is facing the dual challenges of a de-cashing society and non-nationalization of money，making the digitalization of fiat currency an inevitable trend. The digitalization of fiat currencies may seem simple，but boils down to complicated system engineering，requiring rigorous research and with no examples to follow. This paper analyzes in depth the seven key issues to consider in the innovation of central bank digital currency（CBDC）：whether CBDC essentially central bank debt or private debt；should the CBDC be generated in the form of issuance or exchange；should the technical route be based on the account or token；should we adopt a prudent or proactive attitude toward the application of smart contracts；should the operating structure be single-layered or double-layered；should we adopt interest accrual or not；how do we achieve the balance between privacy protection and regulatory compliance.