Embodiments of the present invention provide a method and a related device for generating a group key. The method includes: obtaining a group ID of a group where a machine type communication MTC device is located; obtaining a group communication root key corresponding to the group ID; generating a group key corresponding to the group ID according to the group communication root key; and sending the group key encrypted by using an access stratum key of the MTC device to the MTC device, so that the MTC device obtains the group key through decryption according to the access stratum key of the MTC device. According to the foregoing technical solutions, a base station may allocate, to an MTC device, a group key corresponding to a group where the MTC device is located.