The size of the optical device used in the integrated optical path must be small enough. The traditional coupling beam splitting method requires a long coupling distance, the size is not easy to control in a small range. The use of a coupling region to increase the variable dielectric column can effectively reduce the coupling distance. Straight waveguides are introduced into the photonic crystals, and the exit ends of the straight waveguides are designed as three wave exit ports, where the exit ports on both sides have the same structure. Using the finite-difference time-domain analysis, the results show that the purpose of controlling the power distribution of light waves can be achieved by changing the size of the dielectric pillars in the coupling region between the straight waveguides, thereby achieving the splitting ratio of the waveguide transmission process.