The invention discloses a key updating method for switching a base station eNB in a long term evolution (LTE) system. The method comprises the following steps of: after a target eNB receives a switching request message of a source eNB, transmitting an NCC (Network Control Center) carried by the switching request message to an MME (Mobility Management Entity); progressively increasing the received NCC by the MME for carrying out NH synchronization for the first time; progressively increasing the received NCC once again for carrying out NH synchronization for the second time; returning results of the twice NH synchronization and a corresponding NCC to the target eNB; calculating KeNB* by the target eNB according to the result of the NH synchronization for the first time; and updating the KeNB according to the KeNB* and deducing RRC (Radio Resource Control) and UP keys. The invention also discloses an eNB in the long term evolution (LTE) system, an MME and the long term evolution (LTE) system. The invention can have forward safety of one hop during updating keys, and in the view of a user, the invention provides better security guarantee on the basis of not reducing the operation efficiency.