The present invention provides a method for switching flow in a stacking system, when a new adding apparatus in the stacking system enables the topology to be changed from chain type into ring type, the one stacking terminal of one new adding apparatus is blocked; after the process of each apparatus in the stacking system performs the chain type topology converge, the main apparatus performs recovery configuring for the new adding apparatus; after completing the recovery configuring, the new adding apparatus with one blocked stacking terminal sets the stacking terminal into a forwarding state,the shortest forwarding path based on the ring type topology can be calculated, and a first notifying message changing from chain type topology into ring type topology transmitted by two stacking terminals; the apparatus receiving the first notifying message forwards the first notifying message, after recalculating the shortest forwarding path. The invention can avoid the flow interrupt during the stacking system changes from the chain type topology into ring type topology.