A method for forming an MEMS inertial sensor is provided, comprising: providing a first substrate having a first surface and a second surface, wherein providing the first substrate comprises providing a first base substrate and forming at least one conductive layer; providing a second substrate having a third surface and a fourth surface; bonding the first surface of the first substrate and the third surface of the second substrate together to form a first bonding interface; thinning the first base substrate from the second surface of the first substrate to remove part of the first base substrate; and forming a movable element of the MEMS inertial sensor, wherein the at least one conductive layer comprises a shielding layer, and the shielding layer is located between the first base substrate and the first bonding interface.