Based on photonic crystal multimode waveguides the double-wavelength optical power splitter is presented. The device can be used to divide the input beam equally for both 1.31 μm and 1.55 μm at the same time. The total length of this device is only 15 μm,which is one 182th of the conventional dielectric counterparts reported. On the basis of the guided mode propagation analysis method,the self-imaging effect is discussed for the case of symmetric incidence. The finite-difference time-domain method is used to simulate the propagation of the beam in the multimode waveguide. The results show that the repetitive appearances of single image and twofold image of the input field occur alternatively in this device. The efficiency of the splitter is calculated,and the variation of the efficiency corresponding to the positions of the dielectric rods lying at the junctions between the multimode waveguides and single-mode waveguide is also discussed.