Disclosed are a method for channel estimation in a wireless communication system, and a device therefor. Particularly, the method for estimating a channel by a terminal in a wireless communication comprises the steps for: receiving, from a base station, configuration information for channel estimation, the configuration information comprising relationship information related to the relationship between a cell-specific reference signal (CRS) and a demodulation-reference signal (DM-RS); receiving the CRS from the base station; receiving, from the base station, on a specific channel, the DM-RS and machine type communication (MTC) control information; estimating the specific channel by using the CRS and DM-RS, on the basis of the relationship information; and decoding the MTC control information via the estimated specific channel, wherein the relationship information comprises information about a pre-coding relationship between the CRS and DM-RS, and power ratio information of the CRS with respect to the DM-RS, and the power ratio information is information related to the power ratio between a CRS port and DM-RS port for an idle mode.