The invention discloses a method and equipment for updating an anti-replay parameter during master and slave switching. During master and slave switching, new master equipment sets IPSec SA to be invalid, acquires an anti-replay window and an anti-replay sequence number from opposite-end equipment of an IPSec tunnel to update the anti-replay window and the anti-replay sequence number of the IPSec SA per se, and sets the corresponding IPSec SA to be valid after the update is finished to process data so that the new master equipment can acquire the real and reliable anti-replay window and anti-replay sequence number and the security of data transmission is ensured.