Provided are a method and a wireless device for monitoring a downlink control channel in a wireless communication system. The wireless device monitors a first downlink control channel in a first search space, and monitors a second downlink control channel in a second search space. The first downlink control channel is modulated by a first reference signal, which is generated on the basis of an identifier of a first serving cell, and the second downlink control channel is modulated by a second reference signal, which is generated on the basis of an identifier of a second serving cell.