A plastic surface-relief grating as a wavelength division multiplexer is designed and fabricated with the conventional mould pressing technique using the transmission-type fused quartz phase grating as mask pattern and polycarbonate as basal material. The experiment results show that in an optimizing process, the plastic surface-relief grating has the highest firstorder diffraction efficiency under adequate groove depth and incident angle, and can be used as the best optical path for wavelength division multiplexing (WDM). We also establish the experiment setup for testing the WDM performance of the plastic surface-relief grating based wavelength division multiplexer. The results show that the proposed wavelength division multiplexer has the high-stability temperature characteristics, the low insertion loss of less than 5 dB, the large isolation of greater than 20 dB, the low polarization-dependent loss (PDL) of less than 0.4 dB and the relatively steep pass-band characteristics. It is a WDM device with good performance, which can be applied in short distance communication.