In this paper, we design a novel 2x2 silicon-on-insulator (SOI) wavelength switch photonic crystal included multimode interference waveguide design. With the changes of refractive index of photonic crystal, we can perform the switching function. Applying the configuration of Y branches, the input and output waveguides can be easily laterally separated for direct coupling to fiber without S- bending structure. The 1.55 micrometers wavelength will be switched at different output ports. The output mode patterns and light propagations are simulated by using beam propagation method.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.