A communication method of a terminal (100, 200, 300, 400, 800, 900, 1000, 1300) in a mobile communication system, the method comprising: transmitting, to a base station (152, 252, 352, 852, 952, 1052, 1400, 1700) providing a mobile communication service to the terminal (100, 200, 300, 400, 800, 900, 1000, 1300), capability information including information indicating that the terminal supports a high-speed communication, HSC, mode and a low power and low speed communication, LPC, mode simultaneously; receiving, from the base station, first cell information on a first communication mode corresponding to the HSC mode, wherein the first cell information is used to attach to a first cell related to the first communication mode; receiving, from the base station, second cell information on a second communication mode corresponding to the LPC mode, wherein the second cell information is used to attach to a second cell related to the second communication mode; determining to perform a communication with the base station using the second cell related to the second communication mode, in case that a predetermined condition is satisfied; transmitting, to the base station (152, 252, 352, 852, 952, 1052, 1400, 1700), via the second communication mode, a first message including a terminal identity used by the terminal to attach to a network in the first communication mode, wherein the first message is a report notifying that a cell attach using the HSC mode is unavailable; and transmitting to, or receiving from, the base station, a signal with the base station (152, 252, 352, 852, 952, 1052, 1400, 1700) via the second communication mode using the terminal identity, wherein a coverage of the second cell is broader than a coverage of the first cell. transmitting, to a base station (152, 252, 352, 852, 952, 1052, 1400, 1700) providing a mobile communication service to the terminal (100, 200, 300, 400, 800, 900, 1000, 1300), capability information including information indicating that the terminal supports a high-speed communication, HSC, mode and a low power and low speed communication, LPC, mode simultaneously; receiving, from the base station, first cell information on a first communication mode corresponding to the HSC mode, wherein the first cell information is used to attach to a first cell related to the first communication mode; receiving, from the base station, second cell information on a second communication mode corresponding to the LPC mode, wherein the second cell information is used to attach to a second cell related to the second communication mode; determining to perform a communication with the base station using the second cell related to the second communication mode, in case that a predetermined condition is satisfied; transmitting, to the base station (152, 252, 352, 852, 952, 1052, 1400, 1700), via the second communication mode, a first message including a terminal identity used by the terminal to attach to a network in the first communication mode, wherein the first message is a report notifying that a cell attach using the HSC mode is unavailable; and transmitting to, or receiving from, the base station, a signal with the base station (152, 252, 352, 852, 952, 1052, 1400, 1700) via the second communication mode using the terminal identity, wherein a coverage of the second cell is broader than a coverage of the first cell.