Disclosed are a method and a system for performing handover of a multimode-multiband terminal by using multi-target cells in a mobile communication environment. The method for performing handover of a multimode-multiband terminal using multi-target cells in a mobile communication environment, which increases a probability of handover and improves communication quality by using the multi-target cells in a mobile communication system including a CDMA-2000 system, which includes a base station transmitter and a base station controller and provides a CDMA-2000 service to a terminal requesting connection, and a WCDMA system, which includes a radio transceiver subsystem (RTS) and a radio network controller (RNC) and provides a WCDMA service to the terminal requesting the terminal, comprises the steps of: (a) receiving a WCDMA signal transmitted from the WCDMA system through a WCDMA modem and measuring an energy of carrier/interference of others (Ec/Io) value; (b) turning on a CDMA-2000 modem according to the measured value and entering into an idle state; (c) creating multi-target cell information by monitoring a target cell for handover; (d) requesting handover to the WCDMA system; (e) receiving a handover command from the WCDMA system; and (f) turning off the WCDMA modem and switches a communication link to the CDMA-2000 system through the CDMA-2000 modem.