The transmission characteristics of a 2D photonic crystal waveguide with point defects were investigated by the plane wave expansion method (PWM) and finite difference time domain (FDTD) method. It was found that by introducing two resonant cavities (point defects) in the photonic crystal waveguide, light waves near the resonance frequencies can be totally reflected back to the waveguide. Since the resonance frequencies change with the variation of the refractive index of point defects, this phenomenon may be used to design a tunable optical switch.