Provided are a method for upgrading the CPLD and a CPLD upgrading system, and a computer-readable storage medium. The system includes a baseboard management controller, a master CPLD and a slave CPLD, the master CPLD sends a power control signal to the controller through the slave CPLD, in response to determining that the master CPLD has completed upgrade preparation, the baseboard management controller setting the upgrade-effective signal to an enabled state, to make the slave CPLD lock a current power control signal, and use the current power control signal to control the controller (S101); controlling the master CPLD to perform CPLD upgrade (S102); and when the master CPLD has completed the CPLD upgrade, setting the upgrade-effective signal to a disabled state, to make the slave CPLD release the current power control signal, and use the power control signal sent by the master CPLD to control the controller (S103).