The present invention relates to the field of computers and discloses a method and an apparatus for setting a working mode of a multi-processor system without needing to perform connection setting for processors on multiple boards beforehand, so as to enhance system flexibility. A method for setting a working mode of a multi-processor system includes: detecting, after a current board is inserted into a slot of the backplane, whether an associated board exists on the backplane; detecting, if the associated board exists, whether the associated board is in an independent working state; powering on the current board according to a slave working mode if the associated board is not in an independent working state, so as to work coordinately with the associated board; detecting, within a predetermined detection time if the associated board does not exist, whether a board is inserted into another slot of the backplane except the slot of the master board; and powering on the current board according to a master working mode if it is detected that the board is inserted, so as to work coordinately with the board in the another slot. The present invention is applicable to a multi-processor system.