GaP/Si is a promoting heterostructure for Si-based optoelectronic devices since lattice constants of GaP and Si are so closed that they can match with each other. GaP was successfully grow on (100) Si subtracts by Gas-Source Molecular Beam Epitaxy (GS-MBE) in the study. The GaP/Si heterostructure was characterized by X-ray double crystal diffraction, Auger electron spectrograph, X-ray photonic spectrograph and photoluminescence (PL) measurements. The results showed that the epitaxial GaP layers are single crystalline, in which a (parallel) and a (perpendicular) are 0.54322 and 0.54625 nm, respectively. The peaks in PL spectra of GaP epitaxial layer grown on Si are 650, 627 and 640 nm, respectively. The study demonstrated that GaP/Si is a kind of lattice matched heterostructures and will be a promoting materials for future integrated photonics.