Disclosed are a cable modem and a data receiving method thereof. The cable modem includes a downlink channel retrieval processing unit to retrieve a downlink channel, receive an entire channel information message through the retrieved downlink channel, and receive a broadcasting supplementary data message when the entire information message is valid; a channel information processing unit to receive broadcasting supplementary data using the broadcasting supplementary data message; an uplink channel retrieval processing unit to retrieve an uplink channel using the entire channel information message; and a channel information managing unit to store and manage main data receiving channels capable of receiving the entire channel information message and the broadcasting supplementary data.