an electronic ledger system generated by the full face information of invoices issued by taxpayers. The billing system has established a timely, complete and accurate electronic billing database for invoices, that is, the billing information database. The full face information of invoices issued by taxpayers, including Chinese characters and digital contents, will be encrypted and uploaded in real time to generate an electronic billing system. The use of the ledger system involves three levels: the first level of invoicing: all enterprises have to invoice through the VAT billing system, and this invoice information will be transmitted to the electronic ledger system. The second layer of storage: the electronic ledger system receives the invoice information of all companies, which is networked nationwide. The third layer of screening: the tax bureau can analyze the data in the electronic ledger through various technologies, which is an important tool for checking and selecting cases.