The present invention provides an optical wavelength division multiplexer, which reduces crosstalk signal noise between channels, has good isolation, and has low temperature and wavelength correlationinsertion loss and low manufacturing cost, can be integrated into a multi-wavelength single-channel optical path, to achieve stability and reliability of long-distance transmission of optical signals. The multiplexer comprises a first polarization beam combining structure, a second polarization beam combining structure, a third polarization beam combining structure, and a polarizer, wherein the first polarization beam combining structure, the second polarization beam combining structure, and the third polarization beam combining structure respectively includes two incident portions and an emission portion, and the two incident portions of the first polarization beam combining structure respectively receive corresponding light beams of a first optical signal channel and a second optical signal channel, the two incident portions of the second polarization beam combining structure respectively receive corresponding light beams of a third optical signal channel and a fourth optical signalchannel, and front incident positions of the polarizer are respectively arranged with the first polarization beam combining structure, and the second polarization beam combining the beam structure.