A method, an apparatus, and a system for configuring a key are provided. The method includes the following steps. A mobile node (MN) and an authentication authorization accounting home server (AAAH) generate a domain specific root key (DSRK) of a visited domain respectively. The AAAH sends the DSRK to an AAA visited server (AAAV). The MN and the AAAV generate a domain specific media independent handover service root key (DS-MIHS-RK) by using the DSRK respectively. The AAAV sends the DS-MIHS-RK to a visited domain media independent handover (MIH) authenticator. Thus, cumbersomeness and risks of errors in configuring and authenticating a password manually are avoided, so that large-scale and secure deployment of the MIH service becomes possible.