A method for generating and distributing MIP security key after Re-Authentication, including: an AAA Server generates an EMSK during a Re-Authentication process; the MS generate a new first MIP security key for the MS according to the EMSK, and replaces the corresponding old first MIP security key with the new first MIP security key; and a HA receives new second MIP security key information for the HA which is sent by the AAA Server actively, or requests from the AAA Server the new second MIP security key information for the HA, and replaces the corresponding old second MIP security key that is locally stored with the new second MIP security key that is sent by the AAA Server actively or requested from the AAA Server. The present invention ensures execution of MIP Registration process after Re-Authentication.