A method and a system for managing the power of a DBDM terminal. The method includes monitoring an event occurring when a portable terminal enters into a portable Internet mode; checking a power saving mode when occurrence of the event has been detected; transmitting phone information regarding the portable terminal to the mobile communication base station and the portable Internet base station when a phone on/off mode has been confirmed to be the power saving mode, interrupting power supply to the mobile communication unit of the portable terminal, and entering into a portable Internet mode; monitoring an incoming call request in the portable Internet mode; and supplying power to the mobile communication unit and entering into a mobile communication mode when the incoming call request has been detected.