The present disclosure provides a method for forming and controlling a molecular level SiO2 interface layer, mainly comprising: cleansing before growing the SiO2 interface layer, growing the molecular level ultra-thin SiO2 interface layer; and controlling reaction between high-K gate dielectric and the SiO2 interface layer to further reduce the SiO2 interface layer. The present disclosure can strictly prevent invasion of oxygen during process integration. The present disclosure can obtain a good-quality high-K dielectric film having a small EOT. The manufacturing process is simple and easy to integrate. It is also compatible with planar CMOS process, and can satisfy requirement of high-performance nanometer level CMOS metal gate/high-K device of 45 nm node and below.