SrTiO3 films with different cation concentration were deposited on Si(001)substrates by oxide molecular beam epitaxy.An amorphous layer was observed at the interface whose thickness depends on the oxygen pressure and the substrate temperature during growth.Although lowering the oxygen vacancy concentration in SrTiO3led to better insulating performance as indicated by the lowered leakage current density of the heterostructure,the dielectric performance was deteriorated because of the thickened interfacial layer that dominated the capacitance of SrTiO3/Si heterostructure.Instead of adjusting the oxygen vacancy concentration,we propose that controlling the film cation concentration is an effective way to tune the dielectric and insulating properties of SrTiO3/Si at the same time. SrTiO3 films with different cation concentration were deposited on Si (001) substrates by oxide molecular beam epitaxy. Am amorphous layer was observed at the interface whose thickness depends on the oxygen pressure and the substrate temperature during growth. Almost lowering the oxygen vacancy concentration in SrTiO3led to better insulating performance as indicated by the lowered leakage current density of the heterostructure, the dielectric performance was deteriorated because of the thickened interfacial layer that dominated the capacitance of SrTiO3 / Si heterostructure. Instead of adjusting the oxygen vacancy concentration, we propose that controlling the film cation concentration is an effective way to tune the dielectric and insulating properties of SrTiO3 / Si at the same time.