The beam splitter is the core componen t of the ultra-dense optical path forming system and the key component of the p hoton multifunctional equipment and system.In order to meet the needs of the rap idly increasing data communication services for optical beam splitters,five parallel photonic c rystal waveguides are introduced into complete triangular photonic crystals to form a multi-mode interference system, and a new four-port beam splitter of two-dimensional triangular photonic crystals is proposed by coupling the multi -mode waveguide with the self-imaging effect and the microcavity.Finite difference time domain (FDTD) m ethod is used for simulation analysis, and the results show that by changing the radius of the medium column in the fou r coupling microcavities at the output end,the beam splitter can have high transmittance and realize the average distr ibution of output energy or free distribution within a certain range.