The present invention pertains to a method and device for preserving mobility information in terminal state transition and effectively re-accessing in a heterogeneous cell network in a mobile communication system. A method for estimating a mobility state of a terminal in a mobile communication system according to one embodiment of the present invention may comprise the steps of: receiving, by the terminal, system information from a serving cell during an idle state; calculating mobility state information by using the received system information; storing the mobility state information; and transmitting the mobility state information to a base station when the terminal is connected to the base station. According to one embodiment of the present invention, when an idle state of a terminal is changed to a connection state in a mobile communication system, a mobility state of the terminal can be more effectively estimated.