A method for line initialization performed by a communication device, the method comprising: sending a first probe signal in a downstream direction to acquire a first precoding matrix needed by a first part of subcarriers of all available subcarriers (S 401); sending, by using the first part of subcarriers, multiple data signals of all data signals that need to be sent in an initialization process; after the multiple data signals are sent by using the first part of subcarriers, sending, by using at least a second part of subcarriers of all the available subcarriers, a second probe signal in the downstream direction to acquire a second precoding matrix needed by the at least second part of subcarriers; and sending, by using the at least second part of subcarriers, remaining data signals, exclusive of the multiple data signals, of all the data signals that need to be sent in the initialization process, to complete line initialization, characterized in that: the first part of subcarriers are a set of subcarriers whose center frequencies are not greater than a designated cutoff frequency in all the available subcarriers; and before the step of sending, by using the first part of subcarriers, multiple data signals of all data signals that need to be sent in an initialization process, the method comprises: acquiring a range of the first part of subcarriers according to the designated cutoff frequency; and in a handshake, notifying a subscriber end device in the downstream direction of the range of the first part of subcarriers, or after a handshake is completed, notifying a subscriber end device of the range of the first part of subcarriers when a first data signal of the multiple data signals is sent by using the first part of subcarriers. sending a first probe signal in a downstream direction to acquire a first precoding matrix needed by a first part of subcarriers of all available subcarriers (S 401); sending, by using the first part of subcarriers, multiple data signals of all data signals that need to be sent in an initialization process; after the multiple data signals are sent by using the first part of subcarriers, sending, by using at least a second part of subcarriers of all the available subcarriers, a second probe signal in the downstream direction to acquire a second precoding matrix needed by the at least second part of subcarriers; and sending, by using the at least second part of subcarriers, remaining data signals, exclusive of the multiple data signals, of all the data signals that need to be sent in the initialization process, to complete line initialization, characterized in that: the first part of subcarriers are a set of subcarriers whose center frequencies are not greater than a designated cutoff frequency in all the available subcarriers; and before the step of sending, by using the first part of subcarriers, multiple data signals of all data signals that need to be sent in an initialization process, the method comprises: acquiring a range of the first part of subcarriers according to the designated cutoff frequency; and in a handshake, notifying a subscriber end device in the downstream direction of the range of the first part of subcarriers, or after a handshake is completed, notifying a subscriber end device of the range of the first part of subcarriers when a first data signal of the multiple data signals is sent by using the first part of subcarriers. the first part of subcarriers are a set of subcarriers whose center frequencies are not greater than a designated cutoff frequency in all the available subcarriers; and before the step of sending, by using the first part of subcarriers, multiple data signals of all data signals that need to be sent in an initialization process, the method comprises: acquiring a range of the first part of subcarriers according to the designated cutoff frequency; and in a handshake, notifying a subscriber end device in the downstream direction of the range of the first part of subcarriers, or after a handshake is completed, notifying a subscriber end device of the range of the first part of subcarriers when a first data signal of the multiple data signals is sent by using the first part of subcarriers. acquiring a range of the first part of subcarriers according to the designated cutoff frequency; and in a handshake, notifying a subscriber end device in the downstream direction of the range of the first part of subcarriers, or after a handshake is completed, notifying a subscriber end device of the range of the first part of subcarriers when a first data signal of the multiple data signals is sent by using the first part of subcarriers.