The effects of interfacial diffusion of InGaAs/InP heterojunction on the electrical and optical properties of InGaAs epitaxial films grown by all-solid source molecular beam epitaxy （MBE） are investigated. The InGaAs thin films are studied by X-ray diffraction, variable temperature Hall and photoluminescence （PL） measurements. It is found that inserting a layer of InGaAs transition layer grown by As₄ between InGaAs/InP interface can significantly improve the electrical properties of the InGaAs epitaxial film （grown by As₂）, and its low temperature mobility is significantly improved. At the same time, the abnormal blue shift of the PL peak disappears with the improvement of InGaAs optical properties. The research shows that the growth of InGaAs transition layer by As₄ can significantly reduce the abnormal diffusion of As in InP and obtain a sharp InGaAs/InP interface, thus improving the electrical and optical properties of InGaAs films.