The present invention discloses a line driver for a communication system with a variable loading. The line driver includes a positive output terminal, a negative output terminal, a plurality of current cells, for generating a plurality of output currents, and a plurality of switches, for controlling a number of connections between the plurality of current cells and the positive output terminal and the negative output terminal according to impedance of the variable loading, to generate a total output current such that a output voltage swing stays within a specific range.