A security capability negotiation method is applicable to perform security capability negotiation during a mobile network handover. Moreover, a security capability negotiation system is also provided. Consistent with the provided system and method, it may be unnecessary for the MME to know the security capability of the corresponding eNB in a certain manner during a handover from a 2G/3G network to an LTE network. Meanwhile, during the handover from the LTE network to the 3G network, the SGSN does not need to introduce new requirements.