The combination of photonic crystal technology and THz technology provides a new approach to design novel THz wave functional devices. A dual-wavelength THz power splitter based on two-dimensional photonic crystals was proposed. A directional coupler was formed by introducing three parallel single mode waveguides, and a 1×2 Y-shaped waveguide was introduced as well. Two additional rods were added at the branch of the Y-shaped structure. The coupling lengths for coupled waveguides at different frequencies were calculated by the plane wave expansion method and the principle of directional coupling, and the transmission characteristics of the power splitter were analyzed and investigated by using the finite-difference time-domain method. The results show that the power splitter can split the input field into output port1 waveguide and output port2 waveguide with equal power at frequency of 1.0 THz. However, the input beam can even be split into output port3 waveguide and output port4 waveguide with an arbitrary output energy ratio at frequency of 0.893 THz by asymmetrically changed the refractive index of the two additional rods.