This paper proposes a terahertz demultiplexer based on metamaterials; its unit cell is composed of two layers of "one" shaped metal wires and a quartz substrate in the middle. The terahertz demultiplexer works in the terahertz communication window and demultiplexes two beams of terahertz waves with center frequencies of 0.225 THz and 0.300 THz. The isolation of the terahertz demultiplexer is 34 dB and 47 dB, and its insertion loss is 0.19 dB and 0.04 dB, respectively. The group delay of the demultiplexer was relatively stable. Finally, the influence of the effective and structural parameters of the demultiplexer on its performance are discussed. This terahertz demultiplexer has low insertion loss, large isolation, and stable group delay, and its performance is less affected by parameter changes. It has significant application prospects in practical terahertz communication systems.