A compact and high quality terahertz photonic crystal switch is proposed in silicon. The switch operates based on the self-imaging principle in multi-mode photonic crystal waveguide of triangular lattice. The finite-difference time-domain method and the plane wave expansion method are used to verify and analyze the characteristics of the proposed switch. Numerical simulation results agree well with the theoretical expectation. This kind of device is potentially important for terahertz application and might be a new breakthrough to design other kinds of photonic crystal switches.