Two kinds of plasmonic crystal waveguides at terahertz band are designed and fabricated. Based on the property that the bandgaps of the waveguides can be manipulated actively by varying the air gap between the waveguide, the functions of optical switch and mechanically tunable filter have been realized. The transmission and filtering properties of the two plasmonic crystal waveguides are investigated by terahertz time-domain system. The transmittance is calculated by finite-difference time-domain method. The band gap properties and field distributions are simulated by finite element method. The results indicate that both of the two tunable filters achieve good performance. The extinction ratio of the one-dimensional plasmonic crystal waveguide is 30 dB, the tunable band gap range is 130 GHz, while the range of the two-dimensional plasmonic crystal waveguide is 110 GHz, and the extinction ratio is 40 dB.