Provided are a method and apparatus for generating a key, the method comprising: receiving a first message, wherein the first message comprises a first key generation parameter, the first key generation parameter comprises at least one of a key generation parameter of a first carrier, a key generation parameter of a first default carrier and a key generation parameter of a first initial carrier, the frequency range of a second carrier is a part of the frequency range of the first carrier, and the first default carrier is the second carrier, or the frequency range of the first default carrier is within the frequency range of the first carrier and outside of the frequency range of the second carrier; and according to the first key generation parameter, generating a first key, wherein the first key is a key used by a terminal device on the second carrier. By means of the method for generating a key in the present application, key processing can be performed on a carrier, thus facilitating saving on the signalling overhead and reducing the power consumption of a terminal device where carriers are switched frequently.