We numerically investigate the design of a wavelength de-multiplexer based on a tapered photonic crystal waveguide. The tapered waveguide is generated by reducing the width of the channel which, in turn, provides a gradual change in the effective index for the guided modes. Depending on the wavelength, the grading effect enables the propagating beam to be trapped at different spatial positions along the waveguide. Furthermore, alternation on the tapering angle, i.e. changing the slope of the tapered waveguide, will result in a spatial shifting of the trapping locations. Thus, the structure can be adjusted to pick up the frequencies of interest at the chosen positions. Numerical results show that, by placing vertical line defects as drop channels at specific locations, different wavelengths can be properly guided along the drop channels that are transverse to the main waveguide.