In the process of silicon wet etching, the SiO2 film formed by thermal oxidation is firm and compact, and it is an excellent mask material. However, there are some difficulties in its patterning process. Considering the high density of the SiO2 film, its etching time is so long that the protective layer photoresist wrinkles and floats. In this letter, a novel way is used to achieve the graphical process resorting to the MgO film. A layer of the MgO film as the protective layer is deposited on the surface of the SiO2 film, and inductively coupled plasma etching is used to etch the SiO2 film. Then the chip is put in the KOH solution to fabricate the Si V-groove. The results show that the patterning process is easy to control.