1. A method for establishing an enhanced key when a terminal moves from an evolved universal terrestrial radio access network (EUTRAN) to an enhanced universal terrestrial radio access network (UTRAN), comprising: when the terminal moves from the EUTRAN to the enhanced UTRAN, a target enhanced serving general packet radio service support node (SGSN+) in the enhanced UTRAN deducing an intermediate key used in the enhanced UTRAN according to a mapped traditional key obtained from a source mobility management entity; and the terminal, after deducing the mapped traditional key, further deducing the intermediate key used in the enhanced UTRAN by using an algorithm which is the same as that of the target SGSN+ according to the mapped traditional key; wherein the enhanced UTRAN supports high speed packet access evolution (HSPA+) security function.