The role of total internal refection in photonic crystals multimode waveguides is studied, and the multimode interference situation and self-image using conventional coupled-mode theory are discussed and analyzed. The result shows that the input light still can be propagated with high efficiency down to multimode optical area, and resemble index-guided modes owing to the combination of total internal reflection and distribution Bragg reflection. A total internal reflection multi-mode interference photonic crystal waveguide polarization-insensitive power splitter is designed which has great potential value in the integrated optics.