BMC online upgrading method and device

The invention provides a BMC (Baseboard Management Controller) online upgrading method and device. The method comprises the following steps: transmitting a to-be-upgraded file to a storage medium eMMC (Embedded Multi Media Card) mounted on a BMC system; and executing the upgrading script program, performing version matching, and ensuring that the subsequent upgrading process can be continuously executed after the upgraded version number is higher than the current version. And after the version matching is passed, starting to upgrade the main flash, and after the main flash is successfully upgraded, writing an upgrade success identifier into the upgrade identifier file of the storage medium and restarting the BMC system. The upgrading identification file in the storage medium is read in the system background, if the upgrading success identification is scanned, whether the upgraded BMC version number is consistent with the to-be-upgraded BMC version number or not is calibrated, and if yes, the process of upgrad