The invention provides a secure online 
upgrade method and 
system for tax 
control equipment software. The secure online 
upgrade method comprises the steps that: a terminal sends a tax 
control equipment identifier that is encrypted based on a first key to a network end; the network end decrypts the tax 
control equipment identifier via a second key, and sends a communication key that is encrypted based on a third key, an 
upgrade data packet that is encrypted based on the communication key and a 
digital signature to the terminal, when determining that the tax control equipment identifier is a credible tax control equipment identifier and that the terminal has 
software upgrade authority; the terminal decrypts the communication key via a fourth key, obtains an upgrade data packet 
plaintext via the communication key, obtains a first abstract corresponding to the 
digital signature via the communication key and the first key, and executes an upgrade operation of the tax control equipment 
software, when determining that the upgrade data packet 
plaintext is a complete and effective upgrade data packet 
plaintext according to the first abstract and a second abstract that is calculated based on the upgrade data packet plaintext. The secure online upgrade method provided by the invention is used for guaranteeing the security and integrity of 
data transmission in an upgrade process and reducing the upgrade cost of the tax control equipment software.