We design an elliptical crossing waveguide with high efficiency based on multimode interference (MMI), adding a mode matcher and adjusting the self-focusing position to reduce its transmission loss. The COMSOL simulation shows that the transmittance of the waveguide reaches 96.5% and the crosstalk loss is less than 2×10 -5 at 1550 nm, while the transmittance is 91.2% for traditional elliptical crossing waveguide. The imaging law of elliptical MMI is analyzed theoretically and verified in simulation. The results show that the new elliptical structure not only exhibits high efficiency at 1550 nm, but also has very low loss (less than 0.2 dB) and crosstalk (less than -42 dB) for the whole communication band from 1500 nm to 1600 nm. This cross-light waveguide is small-sized, simple-structured, and is formed by only one step etching with the grating couplers on a silicon-on-insulator (SOI) platform. It has simple preparation process and is conducive to cost savings and mass production. So it will be widely used in integrated optics in the future.